I'm in the process of actually trying to work out what would be feasible performance-wise if I were to spent the considerable effort to add the features required for base D3D support. It's not looking good, unfortunately. Beyond just "shaders", there are a significant amount of other requirements that even just the OS's window manager needs to function at all. It's all built up on 20+ years of evolving tech and for the normal players in this space (AMD, Nvidia, Intel, Imagination, etc.) it's always been an iterative process.