Power?
She was beating Yoruichi, even in speed. In fact, she's one of the fastest characters, and I mean
reallyfast. She was just learning Shunko and that's strong enough to
stun or attack targets with
an exponential combat capabilities increase. Granted, she hadn't mastered it before the time skip, but when she succeeds, she could become one of the strongest characters. As for reiatsu, you don't know that. She didn't show off because she's the leader of the Stealth Ops,
but her Bankai was really powerful, and she didn't get to use Shunko in time. For charisma, you don't know that, but Yamamoto didn't show much either. She's decisive and a good leader though. Her squad is highly disciplined and she only accepts the best from the best. She was on the same level as Yamamoto in her views of order and lawfulness.
Not saying that she's the best for the position, but she's pretty high up there.
Why wouldn't he be interested? He quickly accepted his former position because he was attached to his squad, and his squad accepted him quickly, a squad that was very attached to Gin. And he's a Vaizaado, so his power with the mask on is much higher than just a normal captain. Also, due to his Hollow nature, his Bankai may not be able to be stolen. He's one of those characters with small roles so far though.
She's most likely the best choice. According to the databooks, she might even be a strong as Aizen and Yamamoto. She was also one of the first captains fighting side by side with Yamamoto, she's very intelligent and was the only one to notice Aizen's illusions. Not much else known about her though.
The Vaizaados didn't exactly have a leader. He was acknowledged by them as strong, but as a leader he was just okay. From his role in TBtP, it can be concluded that he wasn't above average in charisma or leadership. The reason Aizen worked under his nose for a decade was because of his lack of interest for his subordinates. He's also kind of immature.
Lack of
power? Lack of reiatsu? We don't even know if he's skilled in Kido, but he's good with Shunpo. An excellent tank too, more so than Kenpachi. Speaking of which, Kenpachi didn't really hurt Komamura, it was sort of an equal fight. Now he's doing good against Bambietta. Komamura is made a lot of fun of, even though he's lost against Arrancarized Tousen and Aizen twice, both whom were many times stronger than a normal captain.
His personality and leadership are excellent. He's the best possible replacement for Yamamoto if not for his power not being the best around.
Shunsui wouldn't take the responsibility of leading an organization. He barely even does anything for his own squad. His experience and strength are not enough to step up for the job.
Why not? He was handling Hollow Ichigo pretty well and from TBtP he seemed competent. Another barely known character though.
He would be a good choice, actually. He's very, frighteningly organized and responsible. His superior intellect and knowledge of the Quincy would make him a good temporal replacement for the time being. He would return to his experiments as soon as he got the chance though.
And that illness is what permanently keeps him away from being a leader at anything. He never attends meetings or manages his squad, and has to be replaced by his subordinates all the time. It's a shame that he's never active because he somehow contracted tuberculosis even though he's a ghost.
But Isshin is a terrible father. He can have his few shining moments but he's just as shady as Urahara, and that's saying a lot.
He wouldn't. He's smart and all, but he's absolutely terrible when given a position of power or control. He couldn't be trusted to look after a mountain.
She's pretty much Soifon but with better control of Shunko and since she's from royalty, her reiatsu might be stronger.
And very fast, bearing the tile of "God of Shunpo", at least before faster characters stepped in. But she's got one big flaw, and it's that she's careless and laid back when there's no trouble, so I can't see her leading SS in times of peace.
I don't know why nobody ever mentions Tessai though. He grew up with Urahara and Yoruichi, was a captain, could cast any Kido without incantation, and has an astonishing sense of responsibility even towards the most trivial things. I get the impression he's forgotten because he has never fought against anybody except for that time he slapped a hollow in the face.