Rift had "support" as a dedicated party role, and it was pretty great. Especially as nobody liked doing it so you basically got to play as DPS but with much smaller queue times Depending on what particular fights required you could focus on buff/debuffs, AOE healing or damage, and if you built your character right you could still put out pretty good DPS while performing your support role, and soloing was never much of a problem. The main problem was that in terms of buffs/debuffs, their usefulness scaled based on party size, so in small groups it was debatable whether it was a benefit, but they were pretty much essential in full raid content - however you never really needed more than one because all their effects were raid-wide.

However, it kind of needs things to be balanced around from the beginning, not just bolted on later. The entire party balance in FFXIV is designed around groups of 4 or multiples thereof, with a 2:1:1 mix of DPS:heals:tanks. You can't just drop a DPS slot and turn it into support without needing to rebalance pretty much every encounter to account for lower group DPS, and conversely you can't increase party sizes to 5 to allow for a support role without accounting for higher DPS.