While it's not conventional emulation, my understanding is that the DirectX 9-11 support isn't very far removed from how shader recompilation works in modern console emulators (RPCS3, Xenia, Cemu, Yuzu, etc.). Steam now even distributes shader archives among Proton users so that they can be translated in advance instead of on-the-fly, which is something that Cemu users had been doing among themselves for a while.
Performance can still be an issue, mostly because the Nvidia graphics drivers are performing worse on Linux vs on Windows.