Extensions?

It looks to me like there's no provision for plugins to JEM, is that right?

I'm interested in using the (very good) registration functions to charge for registration. It's not there now (is it?), but the (almost) vital plugin framework that would be required to allow various payment routes, doesn't seem to be there. Is it?

This could be interesting, yes. As much as I know, this is not possible until now. I think this would be a good enhancement!