Input redirection is mostly unrelated to GPUs, but last I heard (6 months ago, maybe?), this was somewhat stalled -- the first approach, of the server handing off input events to a special client (the compositing manager) and letting it do the coordinate conversions, turned out not to work. (They ran into problems coordinating everyone during e.g. grab handling.) The new idea is for the compositing manager to actually upload a triangle mesh to the server and then have the server use that to do the coordinate transformation itself... but no-one was actively working on this, and there's a limited quantity of keithp-types to go around.
Someone else may have more detailed/up-to-date information.