This will allow for better planning ability and velocity calculations. Teams will hopefully have contributors that will come and go, but also have a core group that is consistently around. Teams will need to be able to calculate their work potential for a sprint based on which regulars they expect to have.
Hey why you add this here!!
Let me know if this is something I should move into bugzilla for implementation tracking.
We were discussing in IRC and I just needed to jot it down before I forgot. Bugzilla takes to long to find the right place to file bugs :)