Given the current state of the likes of Compiz/Mutter, KDE, et al., I struggle to think what effects Unity is possibly going to offer that will be obviously and visibly different on Wayland as opposed to X.org.
The network transparency of X has been criticised in places like Slashdot for years, yet I always understood that this criticism was basically mis-placed: that the protocol itself doesn't particularly impinge on the efficiency of the server at all, and that the problem is more that the basic X protocol was essentially static for years.
We've finally got an X.org project that is kicking ass, modernising the code and the protocols, simplifying and chopping out the crufty bits, but which is still terribly short on hackers. Splitting the stack in two - X.org for compatibility, Wayland for new hawtness - just seems mad.
This is exactly the kind of thing that ought to get cross-distro agreement. If X.org isn't up to the job long-term, then let's everyone set out a roadmap of where we need to go. Let's not have Xgl/AIGLX all over again.