It's not 'conquering' or 'taking' 8 planets in one go, though. This is only rebuilding broken comm stations. It's built into the premise that you have to have already taken the planet and built a fully working comm station there. So you have to move in a colony ship and do it normally for any actual 'taking' of planets. If, later on, that planet gets smashed, this change effectively only means that instead of building a colony ship one planet over, you build a remains rebuilder. (There's not going to be one on the destroyed planet, because if the comm station is dead you can bet that any remains rebuilder or engies you had there bought it already as well) It's a convenience thing that requires less micro clicking, but that's it. You're still building a unit, then sending a unit to the world to make the comm station come back, you're just not having to go to the world after the fact, click colony ship, click comm station type, click spot on map.
I guess in your scenario with 8 planets all down at once and connected to your worlds, yes, you would be able to rebuild them slightly faster than you would otherwise, but it's really just from the reduction of micro. The colony ship goes away as soon as you build the comm station, so once you got one station planted, you can build another colony ship, send it to the next planet, and so on. If cost is a factor, you could add in the cost and time of building a colony ship to the rebuild cost/time on the comm station.
It's not really that much of an aggravation to rebuild the normal way, and I don't know if this would be a pain to code in, but I just don't see it as having much of a real gameplay balance effect if it were to be implemented.