So, I'm overall a big fan of modular X. It definitely makes fixing small bugs within the X source base a lot easier as you (generally) have less to deal with. One of the supposed advantages was that X drivers could just be updated to add support for new hardware. Sounds pretty good.
While the X server ABI is far more stable than that of the kernel, there are still some areas where you can get caught here and this hit the i810 driver recently. It was since been updated to at least not abort when using the stable X server. It looks like these are just the corner cases and that in general, an updated X driver should be able to work with older X servers as long as a little bit of care is taken.
The trickier part is the interaction with DRI — as it currently stands, the actual DRI drivers are in the Mesa package instead of being with the X driver. But the two have to match very closely, thus making it not possible to just do X driver updates.
So much for one of the advantages of modular X. The library situation is definitely better, but there's still work to be done on the driver front. Anyone working on fixing this?