I think that a clan database would be much better, so more or less what was proposed before, a clan tag autobalance rather than a banner balance, i'm sure how easy or effective that is to do, but it's probably a better thing to do in my honest opinion.
Or balance by the sole fact that the player is listed under an official clan in this hypothetical clan database.
And anyone would be free to start a clan, but there could be some drawbacks such as trolling and the likes. So add a fee, say 10-20k. Completely reasonable.
Then I don't know about the banner part or have any particularly logically clear suggestions, but one would be that you have a clan config panel, where you upload banners and update your clan info. Because I'm imagining sort of like what we have in Faction Halls for each clan thread. Similar but not quite like it, more a personal page space for clans in cRPG. You would be able to do some nice presentations and it would benefit the community a lot in the long run. Just a small thing like that, would do wonders.
From this page you handle everything not Strategus, but still clan business. Maybe you could even have a clan account, where anyone in the clan can donate into it for the clan to use as they like. Buy heirlooms for their members, weapons, armours, loaning etc. I don't see any negativity beside the fact that this will make it easier to get heirlooms without retiring. But in my opinion, the price does not outweigh the benefits = better community and better clan cohesion.
Anyway, when it all boils down; this is going to require a lot of coding. (Or maybe not, who knows)
Usually there are never really simple solutions, otherwise a lot of problems we consider small would have been remedied ages ago. SUCH AS LADDERS IN BATTLE AND POLE STUN.