Given that they're fine with adding breaking changes to the protocol, I think it's a shame that they're not supporting multi-screen. This will lead to the same problem with Xrandr based multi-monitor where you get screen tearing with mixed refresh rate displays. I would prefer to see "traditional X11 multihead but you can move programs between screens" as the solution for multiple monitors. Even if it worked like Mac OS X where you can't have a single window span across multiple monitors, it would still be better than the current state of X11.