Would it be possible to add shipyard complexes activities to the "Player Race Production Overview" window? Adding slipway constructions, retoolings and the 1000/5000/10000/etc buildups to the "Shipbuilding" tab would be nice, along with the continual expansion up to a certain cap if you implement that, of course.
Since you're adding variant starts rules now, how about one that turns Jupiter into a small red dwarf, making the galilean moons inhabitable or close to? Oops, typing it now I remember how different are secondary stars treated from planets, might not be the easiest addition.