It would be nice if the inserted portion of a custom could be removable. That way a manufacturer could sell a foam temporary (sent with the original) in case of a bad fit. That way a reshell wouldn't cost a user his/her IEM for an extended period. In fact, a reshell wouldn't be necessary (just a redo of the insertion portion). How about it Heir?
that's a pretty good idea but I can see a problem of 'lining-up' the earpiece to insertion portion... perhaps some universal flexi-fit could be designed so any make could be conjoined... your conception should be explored imo.