Tomeu says that a lot of code can be reused from WebCore without problems, but they’ll need to do some mildly complex event translation because the W3C API and the one in Clutter (and in XInput and in Gtk+) are very different.
Here you can see a quick demo of a web page drawing the touch events that it receives, limited to 2 touch points because that’s the maximum supported by Tomeu’s hardware.
This is still early work, but once event translation is done, this should be very close to be feature-complete. And a nice side-effect is that given that the touch API in Clutter is so similar to Gtk+’s, it should be pretty straightforward to port it to WebKitGtk+. You can find the code here, but keep in mind that this is very preliminary work.