Vita recieved no support from Naughty Dog, Sucker Punch, Sony Santa Monica, Guerrilla Games, or Polyphony Digital, among other 1st party studios. Vitas 1st party was an absolute joke. Hell, not only did it fail to support 1st party games, it doesn't even support Sony services. PS Vue and  PS Music, were never made available. PS Video never recieved streaming support. PS Now was killed after a short stay. Play Memories never came to the platform either.

Sony threw a few spin offs on Vita built by their B teams, and basically killed support for it within the 1st year. Comparing Sony's 1st party offerings on Vita to anything is as big of a joke as Sony's first party support itself.

A Sony handheld that shared its library with the home console would have a major advantage over the PSP and Vita. 

First Party is personal opnion, I for one buy Sony systems for what is in my eyes the best 1st party in the industry. The addition of having the option to play 99% of 3rd party titles is a nice bonus.

As for 3rd parties and a PS5 portable. Considering a Portable only needs to play games at 720p to look incredible thanks to the 5 - 6" screen, I don't think devs would have much issues with running their 4K  home games on a portable PS5 in 720p. Scalability is already part of all 3rd party games since they are built for PC. They already have assest for stupid low resolution, textures, lighting, geometry, and such, which even a PS5 Portable would not hit the bottom of.

At 7nm there is no reason for such a device to be any bigger than the orginal Vita, and cost any more than $400. You have to remember consoles and handhelds are sold at cost or a loss as opposed to things like phones, tablets, and laptops selling at 2 to 3 times cost. Hell even the current PS4 Slim would be tiny if you gave it an external Power supply, and ditched the Blu-ray drive since that is how any laptop is built now days. They could sell a PS4 Tablet with a 10" screen right now at $400 if they wanted to.

So Uncharted Golden Abyss, Killzone Mercenaries, Little Big Planet, PS All Star, Gravity Rush, Wipeout are just illusion shovel games. Also, remember vita is 250$ with a memory card required, combined total is ~300$ at launch and Vita is only ~ 35 Gflops while ps3 is around 180 Gflops. Yeah, they can make a portable ps4 at 400$ and it won't be anywhere close to ps4 power just like vita which is the strongest handheld when it came out. One more thing, who is provide the chip for Sony? Not Nvidia since they set the deal with Nintendo, so AMD? Does they have any mobile chip that can play ps4 game at 250$ on the go and last 4 - 5 hours like you people said?

Uncharted Golden Abyss was developed by Sony Bend, they have been developing spin offs for PSP and Vita for a decade.

Killzone Mercenaries was built by Guerilla Cambridge, the B team. 

Little Big Planet Vita was farmed out to external developers. 

PS All Stars, Gravity Rush, Wipeout, Hot Shots Golf, are all niche titles in Sonys line-up. Great games to fill out a platform, but nothing that is going to make people go out and buy a device for.

As for your PS Vita to PS3 comparison, for one PS Vita came out 5 years after PS3, and we are looking at 6 minimum before this would even be realistic. Also, PS3 had the most powerful CPU and GPU available when it launched, compaired to PS4 having an underpowered mobile CPU and a Middle Range+ GPU. 

AMD can deliver a chip right now that offers a CPU multiple times more powerful than the PS4's with better than XBO level GPU power at 15 Watts. Shrink that down to 7nm in 2019, and add an even more effecient Ryzen design and Navi based GPU, and they will have a chip with an even greater performance gap on the CPU side, and well above PS4 level GPU with less than 10W power consumption. 

Then there is always the option of making a super effecient version of the PS4 APU at 7nm. AMD can use the knowlegde they have learned in CPU and GPU effeciency, and implement those techniques into the PS4 Super Slim APU, just like we saw them do adding technology to the PS4 Pro revision. 

Sony can either build a PS4 Portable/Switch/Phone or a PS5 Portable/Switch/Phone by 2019 - 2020. Getting PS4 level power in a mobile device will be no issue at all. Reaching a $400 price point will not be an issue either. If they go the PS4 Super Slim and PS4 Portable route,it would use the same chipset, which the PS4 Super Slim should be able to be profitable at $200 or less by that point. The biggest additional cost would be going from HDD to SSD, but Samsung has claimed that the HDD and SDD price gap should be close to elminated by 2020. People are really decieved by these phone prices, which are actually sold 3X or more beyond the cost of manufacturing. 

Uncharted Golden Abyss was developed by Sony Bend, they have been developing spin offs for PSP and Vita for a decade.

Killzone Mercenaries was built by Guerilla Cambridge, the B team. 

Little Big Planet Vita was farmed out to external developers. 

PS All Stars, Gravity Rush, Wipeout, Hot Shots Golf, are all niche titles in Sonys line-up. Great games to fill out a platform, but nothing that is going to make people go out and buy a device for.

As for your PS Vita to PS3 comparison, for one PS Vita came out 5 years after PS3, and we are looking at 6 minimum before this would even be realistic. Also, PS3 had the most powerful CPU and GPU available when it launched, compaired to PS4 having an underpowered mobile CPU and a Middle Range+ GPU. 

AMD can deliver a chip right now that offers a CPU multiple times more powerful than the PS4's with better than XBO level GPU power at 15 Watts. Shrink that down to 7nm in 2019, and add an even more effecient Ryzen design and Navi based GPU, and they will have a chip with an even greater performance gap on the CPU side, and well above PS4 level GPU with less than 10W power consumption. 

Then there is always the option of making a super effecient version of the PS4 APU at 7nm. AMD can use the knowlegde they have learned in CPU and GPU effeciency, and implement those techniques into the PS4 Super Slim APU, just like we saw them do adding technology to the PS4 Pro revision. 

Sony can either build a PS4 Portable/Switch/Phone or a PS5 Portable/Switch/Phone by 2019 - 2020. Getting PS4 level power in a mobile device will be no issue at all. Reaching a $400 price point will not be an issue either. If they go the PS4 Super Slim and PS4 Portable route,it would use the same chipset, which the PS4 Super Slim should be able to be profitable at $200 or less by that point. The biggest additional cost would be going from HDD to SSD, but Samsung has claimed that the HDD and SDD price gap should be close to elminated by 2020. People are really decieved by these phone prices, which are actually sold 3X or more beyond the cost of manufacturing. 

15 watts? Try harder. The switch draws 11 watts docked running full tilt. Probably a lot less portable. And it still only lasts 3 hours.

Edit: in fact, the switch draws 7 watts undocted at minimum brightness.

B team is still Guerilla Cambridge, that is like saying Pokemon Sun/Moon doesn't count because it was made by B team of Game Freak, A team is working on Switch. And yeah, if you think Sony can make ps4/ps5 portable that cost only $250 and last 4 - 5 hours next year then LOL. The strongest mobile chip so far are from Apple and Nvidia, ADM didn't have any mobile chip that can compete with X1 with battery and price, let alone the stronger. But all of sudden, ADM of all people are going to bring out a mobile chip that can play ps5 game cost only $250 with battery 4 - 5 hours. Well, that thing will exist in very far future. At the moment, none portable that can play game of Switch level at 720p/30fps that can last 3 hours and cost $300 only. Maybe wait till Switch 3 or even 4 come out, ps4/5 portable will exist with $250 price have 4 - 5 hours battery. One more thing, 15 watts last 4-5 hours for now exist only in your dream, Switch is 11 watts and last only 3 hours

You clearly ignore all first party games on vita and none of them can sold as sixth as Pokemon X/Y. When combined all, they are not even half of X/Y sales

First party? Lol. Sony's advantage was and is that most thitd party games come to it. With how power sensitive they are I don't think third parties would like a portable version of ps5.

Also good luck with making the huge (in comparison to switch) 700$ ultrabooks into a reasonable size and pricepoint.

The current chip is 15 Watts on 14nm. Like I said, moving to a more refined Ryzen Mobile build, and Navi or newer GPU design, plus the shrink to 7nm you are looking at a massive leap in CPU over PS4 and better than PS4 GPU power at well under 10 Watts.

Using the Switch as an example of the state of mobile tech is not really an indication of where things are. Switch is built on Tegra X1 which is already over 2 years old and built on 20nm fabrication. By holiday 2019 it would be 4 1/2 year old tech.

Killzone is not even close to Pokemon, and Sun/Moon is still a main line title. If Sony bend had made Uncharted 4, and Guerilla Cambridge had made Killzone 3 it would be a totally different story. Still the B team, but a main line entry means more than the team behind it. 

As for the rest, I never said they could build a $250 PS4/PS5 mobile that has 4 - 5 hours of gaming life by next year. I said that the chipset if shared with the PS4 Super Slim should be profitable at $200. Add in the screen, the battery, a 500GB SSD(Flash Storage), and you are looking at a $400 device. Not next year, late 2019 is a possibility though, 2020 would be no issue at all.

Like I said above, the X1 is no indication of the state of mobile tech. The Ryzen 7 2700U is a very impressive mobile chip, and it is just the start. When AMD moves to 7nm and more refined tech, they will see massive gains over even this very impressive chip. Over at Nvidia, Xavier is going to be impressive next year, it will very likely end up outperforming the PS4 on the 16nm fab. Its successor in 2019 will be much closer to PS4 Pro than base PS4.