I can see that working. I can even see easy implementation with this:

The event is done in shatter. To participate, you speak to a npc that lets you choose whom you want to fight for (chaos or cosmos). You can still queue in with the GC of your choice or freelance.

Shatter takes place as normal with one difference: when any ice breaks, a manikin pops out of it. The manikin, just like in dissidia, is an a.i clone (for extra flavor, it takes the shape of whoever struck the ice, like Odin). When its defeated, points are awarded to both sides. The point system is the same as shatter.

When shatter ends, players are given special currency, which they can exchange for various dissidia paraphernalia (music, minion, etc)