Unfortunately Gamers Nexus has stated that new OLED screen will not be compatible with the old models. Perhaps there could be a third party solution though.
Yep. They've said that basically no internal components are cross compatible between original and OLED steam decks. Everything's been redesigned internally
@jayandp@Pistcow and this is OK, normal hardware iteration. Me with the old Deck is still satisfied, can play the same way the same things with same ergonomics. For new players - yes, the upgrade seems much better for the same price (no like Nintendo did, by the way).