What about the introduction of mines, mine layers and mine clearers all as a part of planetary defences/invasion - if you dont take ships to clear the mines around a planet the blockading ships will suffer damage/destruction. 


I would like to see this new ship type introduced to add some variation to an invasion fleet. You could even mine the ends of wormholes/jump routes.


Minefields and mine laying were used to great effect in Stars! (where admitedly ships travelled around without jump lanes) - the more mines you laid the bigger the minefield became. Mines placed at the ends of entry points to systems could also be used to great effect in Space Empires IV to protect systems from invasion.