It'd be interesting but the game really isn't built for it and I doubt Heavensward will change it, maybe by 4.0. The way it is now support abilities are spread all over every class, a lot of these are general use and can support everyone. Then there's also the synergy between classes like Dragoon and Bard, both Tanks supporting each other, and Monks supporting themselves.

I actually kinda like the way that works even if it could be expanded upon, still I wouldn't mind a dedicated buffer and debuffer. Dunno how it'd actually work say when you're soloing stuff doing leves and what not and DF queues would have to be changed to accommodate that extra support slot, that last thing sounds like too much work that could be worth it, but this game already puts minimum effort into a lot of stuff.