While new roles would be interesting, this won't work in this game.

FFXIV is locked into the holy trinity of classes: tank, healer or dps. Those are the core functions of classes, but they can branch out a bit to include support skills such as buff(brd, dnc) or debuff/CC(stun, interrupt, slow).

Going with anything besides the holy trinity would require a re-write of the whole game:

What slot would it take? If we're going with the standard 4-man party need would need to be a dps as the healer and tank slots are required. Then for the new role it would need to boost the power of the party by a factor of 1 dps to not be a downgrade for the party.

Give it a new slot so parties are now 5-man, then all dungeons and 4-trials need to be readjusted for 5 people instead of 4, and will that make a full party 10 people?(2xlight parties)
Is the new slot locked for this new role like healer and tank? Then we would see even longer wait times for dungeons.

Just a few of the problems a new role would introduce in this game.

The only real option we have is our current system(role + some support abilities).