Bill, I really don't think this is a new restriction on mainland. The 5 years limit has been around for a while, but it has not been enforced...just like the 60 years age limit that began being enforced a few years ago. From my very experience, the local authorities and employers are worried about so many foreign "experts" that know so much about their culture and them. They want some fresh "experts" to abuse. However, there're some happy foreign campers on mainland and they'll probably tell you otherwise. Some of these may be satisfied as they've satisfied their local lords and the local lords've satisfied them. I think that if the local lords have connections, the foreign experts thick skin and/or some luck, it all can work out well and for a long long time..more than that 5 years.
Cheers and beers