On that subject, you could shape an "AI world" within a level by having an AI-only collision (since special collision groups can now be made) and script zone mesh to funnel AI into specific parts of a map, say for example, only bases and on roads between said bases. The script zone part of this mesh would be a flare-or-no-flare script, so any spawned AI would always land within the "AI world" area.
This should theoretically, allow for an AI that can navigate to key objectives, while ignoring vast map backdrop areas, and not requiring map-wide pathfind generation.
Alternatively the collision part of this could be handled like water used to be handled pre-light solve fix; Place it during pathfind generation, remove it afterwards.
The flare-or-no-flare script zone should be a little smaller to fit within the "AI world" region of the map, so that the AI isn't likely to spawn just outside the edge of where they should be, although this particular issue completely depends on how the AI is spawned via cinematic effects.
Edit: That said, I don't think you want the AI to attack an enemy base on it's own. Any AI units that could be spawned should probably more serve a guard duty role, so a team can use them to build up security in their own base, or spawn some on a map objective, or inside the enemy base as a distraction (they should probably be set to ignore AI Ore Trucks otherwise they will basically do nothing useful). Good example; You captured an Oil Derrick on Pipeline, you spawn a flare calling in ~2 AI bots to then protect it from lone enemy Engineers.