Given how The Witcher 3 ran on WINE and later flawlessly in Steamplay Proton.

Assuming the engine and graphics API hasn't changed, it should work. I'm not sure if the game will exclusively use DX12, given how there are still a decent contingent of Windows 7 users in PC Gaming (around 20% of the Steam Hardware survey last I checked), then it'd be logical to add in DX11 support, which is what Proton is compatible with.

Aside from that, there's also other projects to emulate DX12, although I don't think they're at the same point that DXVK is with DX11.