They gotta figure out how to implement proper Support before going for it. I still say the best way they can do it is by simply have 3 Roles for the "Casual" content and 4 Roles for Savage/Extreme content. So if we currently have
Tanks, PLD/WAR/DRK
Healers, SCH/WHM/AST
DPS, NIN/RDM/SAM/DRG/MNK/SMN/BLM/BRD/MCH

They could potentially have it where
Support, BRD/SMN/RDM

Have it where in Savage content they have access to "Off-healer" support and a Raise ability taking the place of the 2 "healer roles" and instead having 1 main healer and 1 support that provides some healing but also buffs the group to help ease the amount of healing needed on top of granting enhancements.

Though I guess if you want to go a step further and just for fun, Create another 5th role, an off-tank roll taken by NIN/SAM/MNK so now you have,

PLD/WAR/DRK
SCH/WHM/AST
BRD/SMN/RDM
NIN/SAM/MNK
BLM/MCH/DRG

Which could potentially add interesting depth to the game for Savage/extreme content cause now you have 1/1/1/1/4 in terms of party composition and each off-tank could have it's own unique abilities to help ease the dmg the tank is taking while also using support abilities to intercept attacks and gaining a perk if they do successfully intercept attacks.

Now this does mean that certain jobs aka BRD/SMN/RDM and NIN/SAM/MNK would need tweaks to their abilities when doing casual or savage/extreme content but if implemented right the added roles allow the devs to create new content that challenges the users, since it's adding 2 new responsibilities.

I just think there is potential to add new challenges to the game but they do have to take risk with party composition and adding new roles for specific content. Much like how POTD uses aetherpool to determine ones strength rather than their actual gear, Savage/Extreme content could be fine tuned to create that extra depth of difficulty by adding more puzzle pieces to the mix for people to figure out which party composition would work best for them.