Heh. This is already done, but it doesn't quite function the way you're thinking.
Each Actor has a Command and Control level. Upon initialization, each Actor is chained to the nearest unit that is one level above it in the command structure (you can assign units manually as well, for finer control). Each Actor receives its orders from it's immediate commander in the chain. You can have multiple levels in the structure. Thus, you can issue an instruction to the entire army by giving the order to the single top-level commander (or commanders). You can also give orders to any Actor anywhere in the chain, which will propogate down the chain.
The problem with FollowTerrain is the it is not responsible (much) for the intelligent motions of the Actors. Its job is to keep all Actors planted on the Ground mesh object, so no one flies or sinks. You give it your Actor's x and y coordinates, and it returns the proper z value to place it on the Ground. Therefore, it needs to be evaluated for Actor individually, as they are each at a different location with respect to the Ground mesh, and at each frame, so you don't get people cruising through hilltops or gliding over valleys due to IPO Curve smoothing.
Thanks for the input, though - I'm glad other people are interest in this besides myself.