I'm with Strid, you wanting the backwards compatibility is fine and all, but you're being incredibly irrational about it.
Once again, it is completely legal for you to just download copies of the games you own on UMD. There's your legal, free, and easy way to keep using all of your UMD games with the new hand held. If you're not willing to take the simple and effective step to overcome your problem, then that's on you, but you can not seriously expect Sony to hold on to a dead format just because you won't move on.
You will still have your PSP to play the UMD's if you don't obtain digital copies of them; just pick which one you want to play that day before you leave the house and take that with you if you don't have enough space in your bag. Also, the bag thing isn't as relevant for resolving the problem of carrying all the UMD's around; men don't typically walk around with a bag to hold their stuff, so half the players would run into space issues real quick.
And Strid, I do share some of your fears about digital-only distributions; but if they just make it so you can "dock" the NGP with your computer, and load/unload games/saves onto your computer, then that would solve that issue. It'd be the same thing I do with my iPhone, I download an app/song, plug it into my computer, and now I have a permanent backup on my hard drive, so I don't care if the internet goes down. I'm also not opposed to them distributing physical media for the games, but not if that's going to be the primary vehicle for distribution.
They also have Micro SD->MSPD adapters, and since you can get 256GB micro SD cards(with 2TB cards being an eventual maximum), space on a card is a complete non-issue. Even if you had to carry around a few of them, they're small enough that they fit in any pocket without problems.