Since this game will be on Windows, Mac, and Linux, it would only make sense to just use OpenGL and drop DirectX, since too many PC devs are using DX9 only which is so much more inferior and limited than new graphics API's (like DX11 or recent versions of OpenGL) For example, I know a flaw of DX9 is that if a game is using deferred rendering, it cannot use MSAA with it. OpenGL just needs to become the standard tbh
The devs said in the live chat that it will probably be OpenGL only since it's slated for Linux, Mac and PC releases.
This was answered in the stream, I think the response was along the lines of "OpenGL unless Dx (IDK which version) turns out to be really simple to substitute" TBH I don't care as long as OpenGL can achieve the same things Dx11 can.
it can the reason why OpenGL should be used is because of how much damage DX has done to non-MS OS's.