ok, then SF slightly predates wayland.. I couldn't find (and maybe I didn't look hard enough) any evidence of SF prior to 2008. My bad.
Anyways, certainly in the early days, SF wasn't in good shape for hotplug, multiple displays, vblank support, and these sorts of things that matter on desktop.
Anyways, re: protocol stability, I somehow doubt you could claim that SF is backwards compatible to SF from 2006. The protocol stability milestone should have mattered very little to something that is distributed and updated in the manner that android is.
And re: abandoning SF and going to wayland.. well, android has made equally big changes in it's plumbing from release to release. So it doesn't seem too big a stretch of the imagination.