New Class system: Support Classes

I've been thinking a lot about support classes.
Parties would be teams of 5 and 10, instead of 4 and 8. The extra players would be support class roles.
I've seen many ideas for this; Strategist, Time Mage, Blue Mage etc.

I think this would be a great mechanic. Support classes could employ buffs, debuffs, light heals and moderate damage. They could even have stances that have long cool-downs so that they have to make tough choices in battle. (Dmg stance, team protection stance, affliction(debuff) stance, etc).

If you employed this new system, classes like bard and summoner could focus more on their dps, and these new classes would fill in the role of protection and support.

It's just an idea, but I think the change to the mmo's standard tank/heal/dmg system would be refreshing and set FFXIV apart from other games.