As far as I can tell the intention is for EXA to replace XAA entirely. As of (very) recently it even does core fonts nice and fast, so unless you rely on things like stipple acceleration (!) I'd say it's getting there quite well.
(downside: it looks like Speedo and Type1 core fonts are about to stop working, as the code to handle them has been torn out of libXfont 1.4.0. I doubt anyone misses Speedo, but Type1 may very well be missed, because they *do* still work client-side.)