I don't see it happening, unless someone with a great deal of programming knowledge and skill manages to make their own optimised branch, but even then it's a lot of effort for potentially very little gain.
Realistically speaking here, the best we can probably expect out of the XD, emulation-wise, is quite good PSP,N64, Dreamcast, and Sega Saturn emulation. (Since these emulation areas still have a lot of room for improvement)
I've tested the latest builds of these, and quite a few games are very fast and playable. (even with the XD underclocked at 1.4ghz)