Just some interesting ideas I had that can add some interesting dynamics.
-have solder barracks with solders in them. solders are only for boarding parties or defending from enemy boarding parties. They can't carry stuff
-these solders can board some sort of small vehicle that sends them to an enemy ship. Then they can sabotage modules and kill crew.
-solders can kill enemy solders that are boarding.
-maybe have small interior turrets you can place to kill enemy solders.
-boarding parties can be shot down when they are flying towards one of your ships.
-also it would be interesting to have a story mode in the future. (Obviously not any time soon.)