I could see this game being set up like a DOTA/head to head Tower defense game.
I wouldn't want that in general, but I think there could certainly be maps created with much fewer construction sites for buildings and a bunch of turret sites. An ally factory set to churn out troopers with a rally point at the enemy base would effectively make a tower defence map (as a separate mode). Tower defence elements in certain maps could add a bit of variety to the main RTS.
