If you're right that swapping HMs midstream is a bad idea, I think you need a better argument than "it's a bad idea." What's the actual danger? If I'm making my own HM I'm already pretty savvy. Why tie my hands?
But yes, if you win that point, I agree with the change to replace setHM(HM) with HM createHM() -- http://groups.google.com/group/Google-Web-Toolkit-Contributors
