Hey, excellent mod that should get a lot more attention.
First, a supercycle, having larger long-duration cycle that varies raid scheduling and size would allow for a better gameplay experience. (Alternating periods of relative calm and heavy raiding gives the player more variety in terms of gameplay, this cycle would kick off with the first raid)
Secondly, night raids (basically a sypercycle aligned with the day-night cycle), you could configure the mod to have heavy raiding at night and less raiding during the day. (The flavor of having the biters come out at night is immaculate and gives the player a clear visual indicator of when they should be worried.)
Thirdly, adaptive difficulty, you could underpin the raiding and expansion systems with a point-buy system, where the biters spend points to execute or augment actions. The biters would gain points (modified by the supercycle) from time, research, pollution, nests destroyed, productivity, etc. Conversely, biters causing damage could subtract points so that the biters ease off after they've done significant damage. Most of this would be configurable. (The points are basically a pressure system, with raids and expansions letting off steam)