I'm starting to see "traffic calming" popup on greenways now, after posting this even. The little plastic poles between the lanes. Wouldn't be surprised to see speed humps or something every so far someday on some of them.
I think the truth some people need to hear is that racing on MUP's is possibly more dangerous than riding on the road with cars. You can kill someone going 20+ mph on a bike.
I'm always a fan of engineering controls before spending effort/money on active enforcement. You can insert enough curves, bumps, whatever to slow a Cat 6 rider's roll.
I also blame American bike racing culture being too much of a "loner" thing that only super fit crazy people do. I get the idea in other countries is much more social and inclusive, meaning more accessible for the average Cat 6 MUP racer.
We need more clubs that do non-USAC affiliated local competition. I think cyclocross and running people do a good job of that.