Oh! very honestly i can agree with most of what you write "dgm"... but isn't one already there ?
Why not "improve substantially" what is already there ? ... "basic" and "incomplete", is already this particular field of "display/graphics" full of!..
Isn't a popular saying full of wisdom; "union makes the strength" ..right ?
Why not merge NX(basically all of it is GPL) with X ? ... why not a "multithreading", "multi GPU aware" X system ?
(can't find anything more enthusiasm/interest giving, full of life and challenging, than this perspective ... only it might need a lot of "union & cooperation", its not for a single mind, for a single individual glory... c'mon it could be perhaps 1/4 1/5 the size of Linux kernel, and this last project is prove that such things are possible)