There's a few mountains that Steam Play Proton still needs to climb over the next few years, to enable more Windows games and more features in those games to work under Linux. One big one is at least in progress.
Ray Tracing being one of the big things in gaming tech now, thanks to both AMD and NVIDIA having Ray Tracing cards out in the wild. With that, we can expect more games to begin using it.
Thankfully, VKD3D-Proton, which is the Valve-funded fork of vkd3d to work with Direct3D 12 has a Pull Request open with the start of the work towards supporting Ray Tracing. Keep in mind though, while exciting for Steam Play Proton users, this is far from complete and not enabled directly for games as of yet as stated in the PR "Don't expose any features to app yet, but allow overriding FL to 12.2 for local testing while bringing up DXR.".
Since The Khronos Group formally released the cross-vendor Vulkan Ray Tracing specification back in November it makes it all possible. Hooking up Ray Tracing for VKD3D-Proton, it will be using those new extensions.
Having DirectX Raytracing working on Linux for Windows games in Proton sure does sound pretty big. Some of the titles using it include: Amid Evil, Battlefield 5, Bright Memory, Call of Duty: Modern Warfare, Control, Deliver Us the Moon, Fortnite, MechWarrior 5: Mercenaries, Metro Exodus, Minecraft, Shadow of the Tomb Raider, Stay in the Light, Cyberpunk 2077 and more.
If you wish to stay up to date with Proton and Steam Play, follow along on our dedicated page.