I fully believe the Deck 2 will be able to play everything the Quest 3 can, power wise. It should even be stronger than that IMO.
The Quest 3 most likely could run Alyx, after seeing the Deck 1 run it at 60fps on VR headsets (albeit on potato mode), and I do think the Quest 3 is better suited to VR than Deck 1. Quest 3 can run the RE4 port at 120fps and over 4k res. I'm not sure how many games the Deck 1 could run at 120fps and 2160p, and again the Deck 1 runs Alyx, so Deckard could definitely run Alyx, Deck is pretty slow at this point, and the next round of handhelds should thoroughly trump it - as if the Ally X and others haven't already - they have.
I think the idea of a VR fork of Steam OS sounds pretty neat. SteamVR / Home is pretty antiquated IMO at this point, and if you've used a Quest 3 enough, the mixed reality / passthrough UI is just so much faster and more modern than Home. There's a lot they could add to the VR frameworks which it is currently missing if they do a relaunch with Deckard.
I'm definitely more excited to see this happening with a $1200 price point than a $300 one. Even if a lot of it gets eaten up by the lens and internal hardware powering it, it sounds like there's still plenty of money left to add some pretty unique things for VR. But we'll see!
I think the only drawback is there's a lot of die-hard PC VR users who don't like wireless/native play, and would 100% use the device wired to a PC, so having $400 or more of hardware in it that they'd never use could seem a bit annoying? I dunno. Certainly I think it will have to show why someone should be buying a $1200 device for PCVR over spending 1/3 of that on an OLED PSVR2.