X-Amiga's display is just generic VESA. Support could be added for new-fangled graphics cards, but I wasn't sure if there'd be any difference in the quality of display (as far as I'm aware, E-UAE supports OpenGL on the Mac only).
You're absolutely right though, it should work on the latest computers. The problem is that I'm working with 'trailing-edge' hardware ;-)
I have to spend some extra time researching and testing...
Trying to stick to the K.I.S.S principle ("Keep It Simple, Stupid") is really hard!
X-Amiga was initially just a study into the smallest possible OS that could run E-UAE. It's intended to be small, simple and unobtrusive. UAE on desktop Linux or Windows do exactly the same thing, but with all the extras!