I wonder if Shunsui will become jaded enough that he'll want to join our inevitable revolution?
My Headcanon:
If you look closely he already is. At least that was my read of things in the last arc.
The vibe I get from some of the oldest captains is that of a weary caretaker.
They've made their peace with the stagnation of the system, they know Central 46 is corrupt and arbitrary, Yama probably knows all the dirt behind the Zero Squad, the Soul King, and Ichibei and they all have too much blood on their hands collectively (or in the case of Yama and Unohana, individually) to just switch streams when there's no stream to switch to.
They're all a little too deep to pull out, and because they either believe in the value of the stability of things as they are, they know how
unbelievably powerful the roadblocks to progress are* or at least understand the utter lawlessness of the (
possible) alternative, they abide the peace, no matter how distasteful it is personally.
Plus, Yama is the lynchpin for this whole deal. At least on this side of Soul Society.
All the Captains that would ever be able to oppose the system have direct personal ties to Yamamoto, asking Shunsui to fight the system is like asking him to kill his master. Because Yama will defend the system with his life. No matter the cost, he's a burning fossil that exists to uphold the order.
*Shunsui knows about Zero Squad, he might not have details, but he understands the power scale if nothing else. Ichibei is (probably) one of the original Shinigami that imprisoned the Soul King in the first place. That's to say nothing of the rest of Zero Squad.
They are physical gods for all practical purposes and everything Aizen did in the series was absolutely necessary to even have had a chance against them. They're no joke at all.
Which is why I hope there's a way to co-op the Noble Houses instead of going to war, because we would lose 90 times out of 80.
EDIT:
Also, we should remember that the one time that Shunsui thought he had a solid suspicion to go rogue,
he and Ukitake blew up the Sokyoku and had a sparring match with Yamamoto.
That was independent of any of the Ryoka, I'm pretty sure.
Shunsui definitely has it in him, but I think it has to be the right kind of rebellion.
He's a romantic, and the Rukia situation was right up his alley. There couldn't have been a better tragedy;
"The loyal soldier come home to be executed."
"She's locked in a cage to repent for sins she hasn't committed, her cell is guarded by the friends she's made in her service, and her executioners are the commanders under which she served. She accepts her fate, with reservation and humility."
That's Shunsui's whole motif. And when the time came he rose to the call, damn near alone with just him, Ukitake and their direct subordinates.
My only point against that is that it was a small rebellion, it didn't threaten any of the institutions of Soul Society existentially (I would say directly too, but the Sokyoku was actually a big deal even if we don't think about it much). The only demand was a fair trial or a more proportional punishment. When that failed, they nullified an unjust ruling by killing their execution tool. Meaning that a death by Sokyoku couldn't be carried out.
Anything Aizen does is going to be a lot more thorough, it's much harder to be diplomatic when your enemies aren't willing to be talked down.
