Like path nodes in the source engine.
This. Exactly this.
What I've been thinking is, the AI path "web" could be created dynamically between node bricks (upon loading the build, or possibly even while building) This way the AI paths don't need to be stored in the .bls file.
I don't think a path system itself would need to be all that complex, really: Each "path" could just be a set of (x, y, z) coordinates pointing to the next path node. This shouldn't cause too many stuck problems for the AI, since as Lordician suggested, paths should only be generated if there is line-of-sight.
If a path node points to several different nodes, the AI could just choose randomly which node to move to next, or it could choose the node that leads in the general direction of the AI's current target.