Call it wishful thinking, call it a hunch....but I think there are many things pointing to Sony releasing new hardware this holiday.

1. The first thing to point out is the lack of Sony's current drive to push the PS4 Slim. There are virtually no incentives going on on them now. Meanwhile Microsoft is spinning like crazy with bundling deals. Why is this? The top layer answer is to say it is because the PS4 needs less incentive to get people to buy it. Yet I think it is more than that. Sony has forgone any new bundles for a few months. As if they are planning to get rid of the sku all together.  Which leads to my next clue....

2. Sony has lowered their original sales projections for the year......why? The PS4 is as hot as ever, especially off of the release of God of War with critical acclaim. The roster of games this holiday also seems plenty strong with Red Dead Redemption 2 coming. Why decrease expectations of the PS4? Well this reaction is often done when expecting new hardware to hit the market that could upset sales. Sony did the same thing a few months before the Switch release, and again before Xbox One X launch. It is highly doubtful either Microsoft or Nintendo will enter any new hardware this year, as they both had consoles debut last year. Any new revisions would anger their bases who just upgraded or bought the new hardware. So the only one of the big three that could do such a thing is currently Sony. The PS4 Pro released 2 years ago now. PS5 is still not greatly to be expected until 2020 by most analysts.

3. Dev Kits have been leaked to have been sent out by Sony. Most have assumed these dev kits to be for PS5. Yet what the rumors also say is that the sent out Dev Kits are not all that more powerful than current gen specs. It is customary that dev kits be MORE powerful than the hardware they mean to build for. It is also customary that these kits go through several upgrades and changes before it is all said and done. What if this is a DevKit not for the PS5, but for a PS4 Portable? It makes so much more sense. The specs put it inline with PS4 powerline. It is too soon to be sending out PS5 devkits anyway, especially if it is not exponentially more powerful than it.

4. Japan gaming market is almost exclusively handheld these days. Sony is a Japanese company. While PS4 has WW appeal, it still isn't quite setting Japan on fire in the sales department. Meanwhile Switch is becoming all the rage, as to be expected. Even if Sony is putting more focus on Western sales, to forsake the handheld market is to completely relenquish Japan to Nintendo.

5. Sony has given up entirely on the Vita finally(yes, it took this long) now that they have announced the end of PS Plus free game support of the Vita. Astonishing it took this long really. Yet Sony has a way of bringing on bad news..... For the last few years Sony does a "Bad Press" dump just before the "Road to E3" happens, . Reason being, they can squash any negative sentiments with the overwhelming positive. Sony Got Days Gone delay, Vita/PS3 support ending, etc out of the way now, So by the time God of War, Detroit, and the big reveals of E3 roll around they sound like a distant memory.

"Forevercloud, you have to be smoking crack if you think Sony will EVER make another handheld again. They have failed TWICE! What would make this any different?"

Well, for one a PS4 handheld would be getting rid of the PSP and Vita's largest obstacles; the splitting of assets and development from the core console. A PS4 Portable would be playing PS4 games, not imitations.  Sony's vision was always to bring console like gaming on the go, and the technology is finally ready to support it. 

"UMD discs and Vita carts were terrible!"

But what if they didn't use them at all? What if the PS4 Portable could use the same digital games you already own? I imagine that the device would be digital exclusive actually.  I think Sony believes the world to be ready for a purely digital gaming device. At least in the handheld space. They have basically been training Vita owners with this for the past 3 years (derth of physical releases but myriad of digital).

"Hmmm....but what about the PS4 console?"

I think the PS4 Slim will be phased/teetered out. PS4 Pro will take it's place as the defacto PS4 console, price drop imminant. While the PS4 Portable slides in as the new hot portable option. That complements but does not overtake the necessity of the core console.  This could explain why they are not pushing the Slim. It will likely go on fire sale (Think $199). Honestly even if they don't liquidate the Slim, this still could be plausible. A $199 slim PS4 slim 1TB(no game) announcment at E3 sounds juicy. PS4 Pro is also due for a price drop. The Pro's main competition is Xbox One X. Yet the X is at a complete disadvantage on price. While the hardware is amazing, it is hard to justify it's power being worth $100 more in the consumer's eye when many of the greatest showpieces of the year will be Playstation Exclusive (GoW, Spiderman, Detroit). Sony could really strike a fatal blow with even a $50 price drop. MS is already selling the X at a loss, so a price drop is not likely, bundling is the best they can do(albeit I have a theory about what MS's plans are to stem the tide:SOON!)

"What is the long game here?"

Well Sony is a Hardware company, they want to sell hardware. They have only recently been pulling themselves out of the gutter financially, and it is largely due to the Playstation brand. While their Cellphones, TVs, and Cameras all suffered huge losses, the PS is flourishing. They are(and should be) finding new ways to bring the PS brand into people's homes. Portability is an untapped market for Playstation right now, regardless of how any previous handheld hardware did. It would almost be foolish not to jump into it.

Thoughts?Concerns?Wishes?

I don't know if they are doing something like you described but I think something is up. A revision is probably coming

A portable ps4 this holiday would be a disaster for the switch.

Hold on, what do you mean when you say that they've lowered their original sales projections? The fiscal year just started; they've only made one projection so far.

There is no feasible method to create a portable device for an economically viable price that would be able to play PS4 games.

Sony is absolutely killing it with the PS4. They have completely dominated the generation. They have zero interest or reason in developing another portable device. It's not happening. Their R&D is going full-blast into PS5 planning, development, and tweaking. They have abandoned the portable market and the latest fiscal report shows that to have been an extremely financially prudent choice.

It was part of the earnings report like a week ago. Trying to find the article I got that from. Stand by.....

This!

You would still need a TDP of around 10-15W to reach PS4 power these days. This would mean that a handheld PS4 would have to be around 50% thicker and twice as large as the Switch just to have a similar battery life. And with such a battery, the device would weight close to 2kg, way too heavy for extended use as a handheld.

@OP: PS4 did lose a bit of steam, just compare the weekly global sales from last year and this year. It got an early lead of 196k with MHW but then steadily lost almost every week to land at 230k below last year's sales 10 weeks later. 

They copied things like rumble, analog and Wii-motes but if they did this... man. Sony would look like clowns. I don't even see why they would. They have the number one console on the market right now and they're taking names with it. There's no need to copy Nintendo's business moves right now.

Ye, till be a backpack where you cna fit your PS4 and take it anywhere you go. I kid, I kid...

Given how long they officially stopped caring about the Vita...honestly I am not sure what they think they can do to break into the market.

They had a window to do so...and Nintendo has pretty solidly taken it. I mean Splatoon 2 is a serious Japanese killer app, and with Monster Hunter currently focusing on a console version they can't exactly get that going.

They'd have to keep the PS-Switch afloat with their own titles...something they have pretty much never done with the PSP and Vita. Without those it would only be really a thing in Japan, and that isn't enough to keep a device like it going.