There is plan to add some advanced logics like Rampant's siege mode, which small groups continuous raid you non-stop for a minute or 2. But implementing Factorio 2.0 features took over that priority. I will revisit it once 2.0 changes are done.
If you find the enemy are not attack frequently enough, you could adjust some map setting to increase the frequency. Here are some of the them you can increase.
"[time base attack] add points by %".
"[attack point] point collector multiplier"
"[attack point - RL]" amount, (adding attack points by launching rockets to space)