I'm going to make one last argument and then I think we will have exchanged enough arguments for council to make a decision later today. 

This is an experiment. We both agree that we need more implementational experience. For now we don't really know if roster size or crypto overhead and crypto operations will be be the bottle neck.

However if we don't know, the most sensible thing from my POV is to keep it simple. Do the minimum viable thing. Take the existing roster, with its existing features wrt groups and stick it into one encrypted item. Allow us to reuse existing parsers. Make a drop in replacement for clear text rosters. 

Cheers

Daniel