This is not directly grapihcs related but about interesting enablers for modern UI's anyway...
XInput2/MPX was introduced already in XServer1.7 and the Linux Kernel has had the multitouch support since 2.6.30. So we should have case closed and a working multitouch solution existing for Lixux environment. Right?
Well, what we currently have are couple of reference implementation done to show of the Linux multitouch capabilities, but the full pipeline coming directly from upstream is still missing. When we are discussing about X we should be capable to support all the different use cases from simple gestures with pinch, all the way to cases where we have multiple user interacting simultaneously with a big multitouch device. This makes things complicated.
From the current reference implementations people at ENAC have been working quite actively around the multitouch solutions - directly on top of Linux + they have also patched the existing evdev to propagate multiple pointers through MPX. Another reference implementation of multitouch X driver is done by Henrik Rydberg - found from here. Still either of these solutions have not made it to official XServer.
Now there has been an discussion ongoing in the xorg-devel mailinglist that there would be now an clear first step to include support multitouch features for X. This first step would be limited to have a single focus / input point with auxiliary information attach to the event. Most importantly X would propagate these events to the right clients.
The solution would be mainly for indirect touch devices (like touchpads), but would also cover single-application input cases. From mobile devices point of view, where we would have a simple window manager with top most application fullscreen, this solution would already be able to cover all your favourite two finger pinch gestures - making this basically a full fledged solution for these kinds of devices.