New type of instance, PvE AND PvP

I have been thinking about this, and i thought it could be cool of they made some sort of instance where 2 groups are competing with each other, taking down bosses, and ending up in the same room, where they have to battle the boss AND each other.

The concept would be that a group signs up for the instance (standard 5 man group) like you do with BG's. Then once 2 groups are ready both groups start at the same time.

You then have to beat 2-3 bosses, loot etc. as any normal instance, but the final boss is a fight between the groups, and the boss...or if one of the groups are really slow, just one group, the winner naturally gets to loot him. It is up to each team to figure our whether they should aim for getting to the final boss fast, thereby hoping to avoid fighting the other team by killing/looting boss before they arrive, or if they should fully heal and buff to prepare for possible pvp and boss fight. hoping to catch the otehr team on their knees.

I thought it could be fun, the last boss should be a bit of a pushover though, but give both honor, reputation and good loot, since a large part of the boss fight would be the pvp fight. The other bosses should give good enough loot, so that theinstance is still worth it, even if they dont win the final boss.