It looks like your assessment of Plan 9 is the same as Rob Pike's: the effort (and impact) of making an OS actually work (drivers, usable GUI, etc.) totally overshadows the effort (and impact) of implementing better abstractions.
That sounds pretty much like why PHP won; the effort of making a programming language work (ie the standard library) overshadows the effort of implementing better abstractions.
http://www.eng.uwaterloo.ca/~ejones/writing/systemsresearch....