i remember the time when the Linux community just had the opportunity to speed up gaming with Gallium nine. it's nearly a native graphics layer to play DX9 games on *nix with less GPU call transition compared to the classic DX -> OpenGL -> GPU driver conversion.
back in 2014Q4, Gallium nine was just merged to the mainline open-source GPU driver (Mesa3D) a few months after the DX9 based, 0.6F version was released.
i helped the community with a bugreport
and the graphical glitches were sorted out in a month. finally the Wine performance was great, i didn't have to boot up W7.
i just noted this, because with DX9 - as Scawen mentioned - nearly anybody can play the game.
sadly if the DX10+ version will in place, people will need the DXVK implementation which works for DX9, DX10 and DX11, but in this scenario Linux gamers will need a DX12/Vulkan GPU, because this implementation transforms the DX calls to Vulkan.
i know it's pretty hard to maintain two DX versions, but can't we fallback the graphical engine/DX implementation to a lower level? effects, objects might miss couple of feature and quality, but might be still renderable.