The first step in making the world you want is to behave in line with that vision. Mark apparently doesn't understand that, having spent the last years creating schism after schism in the Linux desktop world, from Mir to Unity to making their own QML API from scratch and developing a mobile UX behind closed doors separate from work being done in the broader community, he is now suggesting that all the desktop projects should work together towards a common goal.
You first, Mark. You've adopted systemd, and that's a nice step ... how about the rest of the separate silo Canonical stack? Example: Get behind Wayland and you'll have automatically given all the desktop projects a common goal, since the rest of them are already there just waiting for you.
To be honest, the way I read it, what Mark really wants is everyone to use and develop for what his team has dreamed up. That would also accomplish his proposal, I suppose. It would be just like when he was trying to convince every project to adopt not just a 6 month cycle but the same 6 month cycle that Ubuntu was championing. "You change to be just like me and then we'll get along amazingly well," is a common mantra for Mark.
Disappointment does not quite start to describe my feelings about this call to arms. It's the right message, but delivered by someone who does not follow it at all.