I think some of the combinations and ideas could be fun. That being said however, I personally do not want that system in FFXIV ARR. I feel it's too much like the GW2 'no holy trinity' / set class roles. And that is something that FF series have most certainly always had.

That's not to say that Bard and Thief tanking in the old FFXI days wasn't fun. Nor was Monk counter-tanking, but it wasn't really viable. I wouldn't want them to change the game just to make that stuff viable, but that's just me.