I’m not that familiar with WSL, can it interface with libraries like DirectX or Vulkan?

I didn’t know that, thanks! That’s actually very impressive, and given how efficient qemu-style emulators are, I wouldn’t be surprised to see near-native performance despite a little bit of overhead from emulating game logic.

No, not that much. The emulation of the syscalls are specific to Linux, so none of that is usable on Windows. They could reuse the emulator, but it seems likely they would write their own from scratch so they can keep everything closed source. Obligatory: fuck Microsoft.

Well, not exactly… WINE is a compatibility layer for syscalls between the x86 Windows API and (among others) the x86 Linux API, quite similar to how DXVK translates from DirectX to Vulkan.

What proton does is combine utilities like Wine and DXVK into a user friendly bundle, along with contributing substantially to the projects it bundles to make them interoperate well.

This looks to me like they want to bundle another utility, which does fast emulation of x86 user code on an ARM Linux system. Another commentator mentioned they are using FEX for this, which looks to me to do the same core task as qemu-user, but more focused on x86 to ARM and generally user-friendlier. That emulator could then be used to run x86 Wine on ARM.

The way qemu-user and FEX emulate one ISA on another is actually very cool btw. They realise massive speed gains by intercepting syscalls and executing them directly, instead of emulating a whole x86 Linux system.