VRR is a must. OLED is probably a given. I’d even be fine with the same 1280x800 resolution.
Spec bump.
Better buttons. Specifically the dpad; I don’t like it. It’s too mushy and I find I’m getting a lot of false-diagonals. Seriously, Valve, just buy a used Vita on eBay, take it apart and copy the dpad design 😁
VRR/Freesync - 90Hz would be awesome, but honestly 40-60Hz would be fine by me; eliminating the stutter from games that can’t quite maintain 60FPS would be killer.
Spec bump - this is a given. V2 will be faster.
Improved dpad - The current one isn’t great, almost X360-level bad. False diagonals-a-plenty.