My personal opinion is that the frame is a bit of a Trojan horse for widening the hardware they can run games (via Steam) on. With folks playing more and more indie and lower power requirement games, the rise of retroid pockets and Android gaming in general has taken off, and initiatives like gamehub lite have made it possible to run even Skyrim on these low power handhelds.
On the same token, the amount of performance per watt that Apple has been able to get out of custom arm based silicon is astounding. Valve has said they wouldn’t release another steam deck unless it represented a generational leap. That sort of leap would be something like the intel —> m1 that Apple produced.
What’s most exciting for me, is better steam support on multiple architectures. I think what’s most exciting for Valve, is their software and storefront running on more devices and providing a better experience than ever before. From VR to the deck to the desktop to the living room, I think their strategy at this point is pretty clear.
They didn’t really have a choice for the Frame, due to the inside-out tracking features requiring image processing stuff most easily available in those Qualcomm chips. But sure, in a few years when there might be a Steam Deck successor, they will probably weight their options also based on how well FEX did on the Frame. The chances will be probably higher if some 3rd party developers port SteamOS to some currently Android based handhelds.