xserver 1.5.0 is slated as the release with all the ABI breaks. The current planned ABI breaks:
MPX. All functions dealing with sprites and cursor motion (including cursor rendering) gain a DeviceIntPtr or similar argument, to disambiguate multiple cursors. DeviceIntRec is extended to contain a pointer to the device's sprite (I might be able to move some stuff into the devPrivates [whot]). Break with graphics drivers to add a DevInit and DevCleanup to be able to add/clean up after cursors when hotplugged.