So I've had this brewing in my head for a long time.
Essentially the map is a single tower complex in the middle, with sparse cover leading up to it on either side.
And before you ask, yes, I am a professional artist in my spare time.
So each team has their brain inside the basement of this mutually hostile complex. The complex is loaded out with defenses (Both external, like gun emplacements [I was thinking the MG nests from Unitec would be a good use here.] as well as internal patrols by actors and spawners to replenish lost troops within the complex.) and will engage on site the forces of either team that attempts to approach it. Initially the fight will be your forces against tower forces, but as you move inside the complex to destroy the enemy brain and protect your own, you'll also be fighting the forces of the enemy team at the same time. The objective is to delay the enemy team long enough that your own forces will get to the basement first and take out the enemy brain.
If digging in beneath the fort proves a problem (Which I don't think it would, the fastest digger is still probably slower than a direct assault.) you could place mines in the soil around the basement of the fort. I suppose the only problem then would be people flying craft directly into outer defenses, but that could be mostly solved with some creative fort building.
Anyways someone should make this.