I suppose this could be something fun to implement. I too enjoy the Siren's Call battles, the thing I love most about them is seeing the variety that your charging in with/against.
It's be a bit of a problem on smaller maps though, I can already see lag on an enormous scale in places like Caves or Tech maps. Perhaps if it was only limited to outdoor maps? Also, I wouldn't like to 'choose a side' at the beginning of the mission. If your fighting one particular group for three missions, then the option to aid them suddenly pops up, it's gonna be a bit of a confuser.
Username: @Royal
The Alien Tyrant, 357388: Stop the reign of an evil emperor!
Spawning Chaos, 469020: Form an army of Freaks, win the Freaklympics!
The Restarian Front, 363257: Stop the invasion of an alien fleet from another galaxy!
And if there's a story involved in this, I'd probably join too, especially if the whole setup was user-created content. 
I've been wanting and talking about PvP integration in AE since before AE was even announced.
I believe that a Kheldian Gold Standard should be based on SO's, and for anything above that... there's Platinum!
Save Ms. Liberty (#5349) � Augmenting Peacebringers � The Umbra Illuminati
Save Ms. Liberty (#5349) � Augmenting Peacebringers � The Umbra Illuminati
Me and a friend were discussing how much we enjoy the hotspot battles in Sirens Call. It can be very exciting to assist your favorite side in an all out war between factions. Would it be possible to design such a mission in AE? Most times when hotspotting it up you get attacked by other pl. It would be nice to have a chance to setup your own armies of different factions to face off against each other. Maybe even be able to plan in reinforcements after a time limit or once a defeat threshold was met. Maybe let you pick a side at the start or go in as a wildcard able to attack both sides even.
Just a thought.