Hi Matt,
thanks for the note. If MED is the official successor to to MEF3, we could consider deprecating the MEF3 format in BIDS in favor of MED. That is, telling dataset curators to please stop using MEF3 and switching over to MED, **without** invalidating existing BIDS datasets that may use MEF3.
Over there it's easier to tag the relevant people and to cross-link to similar issues and items.
Cheers,
Stefan