Maybe we should have a different kind of large precursor ship that appears at random and spawns Genestealers
Interesting idea. A huge, derelict, ancient alien ship that moves slowly across a system from deep space. Extremely powerful passive defences but you can attempt to board it and learn its secrets. While exploring, perhaps with a Xeno team, there is the chance of predatory alien lifeforms emerging from hiding to attack your team and its marine defenders. The longer your team spends on the ship, the more chance there is of learning some random alien technology. Definite possibilities. The main thing would be to make the defensive technology so advanced that you couldn't simply blow it up, or perhaps have some form of suicide charge so that if you do blow it up there isn't any wreckage
Might have to add an evacuate order so a ship can load ground forces from an alien vessel. Wouldn't be in v5.50 but possibility for the future.
Steve