I think it would be great if there would be a new mission to give the player the oppurtunity to make a homeworld. I think that a homeworld should only be one planet of your own choice and you can make the planet a homeworld with the "Homeworld" ability.
Homeworlds is always you top priority in all of the sci-fi movies and games ect. so therefore i think it should give invincibility and with 200% production bonus. This gives you a much "better feeling" that you can call a planet your home
This would be very cool to add in the game as players can choose thier own home planet, and say that this is where it all begun (even though you got it as your 70'th planet
). But if the player chooses to make another planet their "new" homeworld the current homewolrd will got back to normal, invadeable and with 100% production bonus instead of 200%.