What if all Sony handheld fans want to use it on the go? Bring a BD Drive with them? A lot gamers prefer physical to digital, you know. They even said no physical, no buy.

Depends on how many Super Mario and Pokemon games are on it.

I really hope they can make a PS4 lite, that would be a "PS4 portable". Downgraded visual assets so that the games run in a less powerful device, while not needing to buy the game again in order to play each PS4 game you already have.
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I still think it need Blu-ray Support :)

You transfer the physical disc games from the BD drive (and/or storage) in the dock to the handheld internal storage when it is docked. There is no physical media needed for the handheld when on the go other than expansion storage (micro SD) if you require more space to bring extra games with you.

So digital only on the go like smartphone? Yeah, tell that to all gamers who love physical games. How many people out there want to transfer the physical disc to internal storage when game take over 100GB space? Western AAA games nowadays can take 100 GB data, add on some DLCs and season pass. Yeah, totally possible for it happen in the near future and it will be very successful, only a bit lower than vita

After the transfer you sell the game or give the disc back to your friend since the handheld can't check on the go if you still have access to the disc.

How would the copy protection work with this system? Account binding of retail games via entering a code / CD-key? That would piss off many people.

Regular checks via internet if the disc is still in the docking station? Then you can not switch between games on the go.

The physical game that's in the dock that was transferred to the handheld you mean? Just like the physical game that's in the console that get's transferred to the hdd/ssd? Since the games more than likely won't be running at full PS4 specs, they won't need as much data. That still mean's much larger games than Switch for the most part, so then you need something like, I dunno, a micro SD card, like the Switch. Sizes have been increasing steadily and prices have been falling significantly, especially if you can find them on deal. Right now you can pick up a 128GB for $50, 200GB for $90, 256GB for $150, or 400GB for $250. In a year or two these sizes will be half to a quarter the price, which also means more storage in the handheld itself by then.

Well PS can make it so the disc binds to a max of 1 or 2 account's at the same time when it initially loads the game from the dock onto the handheld. If you have another friend who want's the game, you can delete/transfer the game from your account so they can load and add it to their's, but you of course cannot play anymore unless they delete/transfer it from their account. That way you can share without much hassle. This allows you to share with 1 friend at a time, but as many as you want over time, and also basically stops you from selling the game after the fact, unless it's to a retail outlet that can verify your used game has all account's open to it for the next purchaser. Maybe it also has a transfer button where you can simply input the buyers PSN ID and transfer the game account to them, otherwise people would not want to buy the game privately, not knowing if there were any account's available for it. If you could do this on the spot however, private sales could happen with some confidence, except for the possibility that the copy of the game your selling them isn't the same one that is tied to your account. That's an unlikely scenario, but possible. PS could potentially charge a small fee for this private transaction as well. I think by this time, many PS4 games will be cheap enough that people will still just buy the game directly from retail anyway. You will still get some game sharing regardless. PS5 games being new and more expensive would probably end up being shared more.

Yeah, combine that with $250 portable then it for sure will be more expensive than $300 if they want indie games too. Also, Sony can't compress game like Nintendo to have much smaller data size than from disk to SD card. In 2020, New Switch with new Tegra chip can come out with Pokemon so good luck to that. I still can't understand how ps5 will come out in 2020 with $400 price but PS4/5 portable is only $250 at the same time. Not even Apple or Nvidia can do that. AMD have never ever make the top mobile chip but in 2020 they can make ps5 portable chip cost $250 because you said so. WOW. And the word "probably, maybe" is a wishful thinking for now at best

I have zero desire to play portable systems anymore. So despite in the past me supporting a portable SONY system I no longer do.

The $250 is more so based on using mostly existing PS4 internal hardware. A PS5 Ryzen based unit would likely be more expensive, but not necessarily all that much more. A PS4 SS around 2019 should only cost $199 max, and the portable would only need a screen and battery on top of that, so $250 should easily be doable for the entire handheld and dock. $300 worst case scenario if they were to launch it with a more than reasonable amount of storage. There also would be nothing stopping PS from subsidizing the hybrid $50 to $100 at retail if they feel that's necessary to compete.

Switch also requires micro SD for expansion storage for extra games, and online isn't free, so it's clearly much more expensive than $300 as well. Apparently PS doesn't have the tech to compress as well as Nin does, but there's no saying someone else doesn't, that PS could pay to use. However, Vita game file sizes aren't that large though, like Killzone is 4.0GB and Uncharted is 3.5GB, while Zelda on Switch is 13.5GB. The majority of Vita games look to be around 1.0GB on average. Nin's games also don't tend to have the same level of assets that AAA games have, which allows Nin's games to have smaller file sizes in general.

PS5 costing $400 is a strong guess based on the massive success of the PS4 and much lesser sales of XB1, but we don't know what the cost of it is actually going to be. For all we know it ends up $500, assuming XB2 is $500 since XB seems to be stuck on that price. Maybe PS decides to have a $350-$400 PS5 hybrid and a standard dedicated 4k PS5 home console for $500. I said it "should" be possible based on AMD's newest tech, I never said it was guaranteed to happen, and you have the prices mixed up between different potential portable hardware. "Probably, maybe" seems to fit quite well since it's a post about "if" PS makes a Switch, and "if" it could succeed.