I personally think that ranks and stuff shouldn't be based on character alone. Like, you can't be 'vice-captain level' unless you're the vice captain of one squad or another. So like, titles would be things that can be taken away or whatever. Like, you can have a vice-captain lose his position and be demoted if, say, he's beaten in battle by someone else, who would then take his rank, or replaced by his superior, another player who's gained one of the 13 available 'Captain' ranks.
That way, you could have those badasses, like pre-captain Kenpachi, who are not affilliated with the gotei 13 but are still incredibly strong. Like, if someone had built up their character amazingly strong without ever bothering to advance through the Gotei ranks, then suddenly appears and starts kicking everyone's asses. That'd be pretty cool.
Why So Green And Lonely? We Are Accidents Waiting To Happen.