Ueber-MEPs and points North

For the benefit of those who, through nobody's fault but their own, 
didn't make the last conference call (and for anyone else just reading 
the list and not on the concalls), could someone outline how the new 
"über-MEP" would work?  From context, I gather that it would be composed 
of an "in" segment and an "out" segment, both optional, with "in-only", 
"out-only" and "in-out" falling out as special cases.  Is this basically 
correct?