I am a modder, I developed a dynamic wave generation system last year.

[GrafBlade]

Hell maybe add different attack locations which are randomly rotated through. Where you maybe get some seconds to move over to the Area, just like in Orcs must die,if anyone knows that game.

Never played that game, but you're talking about different bot spawns, so more than 1 or 2, right? Pretty interesting idea as well, but many of current NI maps might be to small and narrow. 
Switching spawns will make it even more challenging for the team, as everyone really needs to participate, especially if maps won't give good possibilities for a base with shieldwall etc. Just imagine a slightly modified Cav map, that doesn't have a proper shielding spot.