This would presumably let x86 windows games run on ARM hardware.
This is almost certainly meant for the next Valve VR headset, but ARM has so much better power efficiency than x86 that a future ARM based Deck would be a huge improvement to battery life.
Also see this tweet:
VR games that have already secretly pushed Android ARM builds onto the Steam Store are ran via Waydroid (androidARM to LinuxARM)
VR games that do not have an ARM build on Steam (windows x86) are being translated/emulated via ProtonARM and FEX
This myth that ARM is more efficient needs to die already. The ISA has almost no impact on efficiency, and especially no impact on gaming, where the GPU is the much more important thing.
I always figured the reason arm chips tend to be more effecient is that theyve been developped for phones