Enforcement, in itself, is just a workaround to ensure compliance. In other words, enforcement is not a good solution. What is needed is a protocol-based solution that works without forking and is non-voluntary.
+1
Why not use MN with X11+ as pool.
Using MNs as pools actually sounds like a pretty darn good idea. Or at least as the backbones of a P2Pool. And then require all mining to be done through P2Pool. You get rid of the MN payment problem and the mining pool centralization problem in one shot. Although this would require a LOT of work and completely re-writing lots of working code.