For some reason the prospect using Wine, Rosetta 2, and DXVK with MoltenVK on top just to run some games doesn't inspire a lot of confidence that this whole thing will be performant and/or stable.
There is also a Vulkan driver for the M1/M2 GPU already, used in Asahi Linux. There's nothing special about Apple's GPU that makes writing a Vulkan driver for it especially hard. Apple chooses to provide a Metal driver only for its own reasons, but they're not really technical.
This wasn't an inconvenience, it was a deliberated decision.
Apples decisions are often wrong when it comes to third party software.
The real barrier is DX games.
Steam frame is more for streaming PCVR than running existing PCVR games natively.
For sure, you can squeeze a few percentage points more out if you optimize for TBDR, and there are some edge cases where it's possible to make TBDR architectures behave pathologically, but it's not that big a deal in the real world.
I also disagree that the Steam Frame is for streaming primarily. If it was, why put such a powerful SoC in it or using it as the prototype device for doing x86 emulation with Fex?
The Adreno 750 is a 3 TFlops GPU that _should be_ substantially faster than a PS4 or a Steam Deck. It'll play plenty of low-end PCVR games pretty well on its own, if Fex's x86 emulation is performant, which it is.
Like the Meta Quest 2, it's a crossover device that a lot of people will just use standalone.