I think it could be a good thing to bring back the tags. Especially in the beginning.
The smaller players could avoid attacking the big alliances by accident. Planets of these big alliances get defence most of the time, which would result in a fleetless player. To be without a fleet that early in the game is quite discouraging.
If a small alliance wants to do a big thing, like take down a planet of the leading alliance, they can just look around in the universe and pick a medium sized one.
Alliance hoppers:
If a big player decides to alliance hop, everyone can see he's without an alliance. A big allianceless player...
Great opportunity for a top20 alliance to do a lemmingrun
and get high xp roids.
And about attacking the big coven planet by big alliances. Think about the bad pr on AD? Everyone knows who attacked him...