> The one place that X could use some updating is all the sync method calls, that unlike RDP become quite slow if the network connection has any real latency.

I wouldn't say the one place, but it is a pain point.

(And actually, many of the supposedly synchronous things are not synchronous at the protocol level, but at the C library binding level -- xlib. Nowadays there's a much closer to the protocol binding: libxcb.)