I don't think it would require too much re-balancing of current dungeons to be honest. It would require some for sure but all of it is currently balanced to include at least one or two BRDs. BRD would remain unchanged really, just a hit to their DPS which could be made up for by giving them songs that boost party DPS when further level caps are unlocked.
If we change the role associated with BRD in the current game we could then ensure every party has the DPS LB which should be the case as it is with a DPS in the party. It wasn't quite as important before/presently since BRD was/is pretty strong. With the reduction of BRD DPS in 2.1, however, getting into a dungeon with 2 BRDs is going to be more painful.
Agreed, it really could but there would have to be some restrictions placed of course. If you allow it to choose between support or healer role when queueing up you'd have to restrict which fairy it can use and possibly require the setting and maintained use of Cleric Stance. Otherwise you're stuck with 2 healers essentially in a 4 man party which could either be really weak or really strong depending. These things are possible to code though and SCH does have DPS spells it could use so it would be interesting to see for sure.
Not necessarily true. You could simply weaken the supporters DPS while supporting in the same way that BRD's songs currently do.