In that same add-on feds should destroy red player/corp figs when they find them, as well as invade red planet(s) when they find them, and pirates do the same to blue figs/planets.

You could set it up so that when they found planets without a citadel, they would claim them and sell off all they could. When they found a sector with multiple planets not overloaded with citadels they would invade one at random, and destroy it(even if it was movable, but maybe not :discuss)

If it is overloaded they invade the most powerful planet, and destroy it.

That all sounds interesting, but it might be better suited for Gold aliens rather than the pirates and feds, since they are invincible. I'm sure players would like the ability to fight back if something is messing with their stuff. But as with Bosses (Feds, Pirates or other custom invincible characters), add-ons will be able to directly control Gold alien movement and actions. So it would be possible to create something like that. Maybe even disable the Feds entirely and replace them with a Gold race that does what they currently do, but can be attacked and their ships captured. Hmmmm.

I thought there could be the possibilty of a 10 sector evil space and an evil stardock ith red ships where red players could go and be protected by these invincible red aliens...

No, I was thinking more along the lines of herding the invincibles into certain area's of space to deal with un-invadable doors.

Could eliminate stalemates. Of course there has to be a limit to the amount of planets they could take a day, and constant regridding(with pers figs) so they cannot move back into your door. It needs more discussion.