Well the next update was going to end midway through your spar with kimiya where he'd reveal his shikai (a sickle and chain type). Aizen would then be presented with the choice to reveal the full extent of his shikai and humilate Kimiya completely (this would lead to him basically going on a psychological death spiral as his inferiority complex drives him, years down the line, to go for bankai training way too early and die). The alternatives were to hide aspects of it's ability resulting in a more even battle, or not using your shikai entirely and trying to eke out a win with kido and shunpo. These two would result in Kimiya, with his confidence restored, becoming less of a shit later in the quest as the eleventh division resulted in him being isolated from the toxic environment of the tsunayashiro family.
If you used your full shikai then Shunsui (who was watching the spar hungover), would immediately sober up and offer to recruit you into the 8th division right then and there just because he realized how much danger you'd be from the upper echelons of soul society trying to monopolize you. This was mostly to give myself an out from writing more academy stuff.
the tournament stuff was a mess for a variety of reasons the primary being the mechanics not handling the power scaling between students with an appropriate level of fidelity and my terrible pre-quest planning in general. Probably the biggest mistake of the quest was introducing that concept in the first place. (incidentally you would have ended up facing yamada seinosuke in the semi-finals, and isshin in the finals).
then would come graduation which was probably the vote I was looking most forward to in all of the quest. Aizen would basically get offers from all 13 divisions but three would stand out: the 2nd, the 8th, and the 12th. You'd also have a vote to persuade one or two of your classmates to follow you with their flexibility based on how much you had bonded with them to that point. for example isshin would probably be down for anything besides the 13th(cause he doesn't want to compete with kaien), and the 1st, 2nd, and 6th because they have a reputation for strictness.
incidentally you'd also have an option for write ins (to ruin my day) and an invisitext option for the fourth division.
a few years would pass and probably a brief mini arc about you getting adjusted in your new division (Though I figured people would want to actually get to more shonen stuff)
at some point around here the interlude with the Quincy elder would happen and soul society would decide to arrest kun quan and give him a (show) trial. A force of shinigami from multiple divisions would be assembled including aizen. It'd be headed by Kiganjo and Tokinada. There'd be a stand off with the quincies held up in a temple and the shinigami surrounding it outside. kenpachi would activate his bankai, a large shield that prevents ranged attacks from occurring in his proxmity, and both forces would engage in close quarters combat. (I also toyed with a three kingdoms esque combat between champions at the gate scenario). Aizen would end up facing up against ka-kui, a quincy youth who couldn't form spirit weapons but had the ability to "improve" things*, and receive the first counter-narrative to the history he was taught about soul society. AIzen would not pay it any mind at the time but after the arc he'd reconsider things.
kiganjo and kun quan would engage in a fist fight, vaguely reminiscent of juuza vs raoh from HnK(regarding the power dynamics not the pathos of course), and Kiganjo would ultimately win bu, because of Kun Quans proficency with martial arts and blut arterie, take so much damage he's basically removed from the fight. His bankai would de-activate and Tokinada would just start wiping quincies out with high level kido. As things go incredibly dire for the quincies, one of them would end up deciding to take as many shinigami with them as possible and pop a bunch of hollow bait.
a hectic sequence would ensue as hundreds of hollows descend the battlefield including a few menos. the swarm of bee hollows would appear along with their mother organism: a floating beehive covered in jagged maws. Aizen would have to decide on his course of action for survival whether it be fighting his way to the fourth division relief camp, staying near tokinada (who is attracting the strongest of the hollows), or something else. I wanted to experiment with giving you nothing but bad choices to choose from but never came up with a specific dilemma.
From here on my plans were even hazier. Aizen'd be rescued at the last moment by your division captain and wake up in the fourth division barracks. He'd find out from someone that central 46 had tried all of the living quincy in absentia as a response to the events of that siege and sentenced them to death. By the time aizen had awaken the biggest quincy groups around the world would be under assault or already wiped out.
At some point the issue of all the shinigami, and hollows killed by quincies during that battle in china was going to be brought up. Probably via offhand conversation, someone would mention how gotei 13 was depopulating settlements in rukongai to return souls to the cycle and restore the balance of spirits.
This is the poitn where aizen would go "what the fuck is this world" and start asking questions and investigating things.
from there the course of the quest would depend on who was in your sphere and what your vision of a better soul society entailed. The endgame would range from a civil war to replace the ossified government to
marching on the royal palace to do... something with the soul king. It'd depend on which division you joined.
If you had joined the second at graduation you'd end up befriending/romancing Urahara and/or yoruichi. With yoruichi on yourside it'd be very feasible to assemble a coalition of nobles willing to reform the government via force if necessary. It'd be very messy of course considering the only ally you could get from the tsunayashiro family was kimiya. If you could convince urahara to have your back the two of you would have like a fifth of the fire power necessary to take on the royal guard. This route you probably wouldn't need to deal with arrancarization at all (but vaizarding yourself would probably be necessary if you actually planned on fighting yamamoto head to head).
Otherwise you'd probably end up exploring hybridization on your own like canon. You'd have to choose between expanding the number of people privy to your plan in soul society(risking detection) or get outside help whether that be recruiting quincy survivors or going to hueco mundo like in canon. You'd get some crazier options if you were working with hikifune in the 12th division (like quincygami and mod soul shenanigans).
if you joined the 8th, shunsui would end up becoming your and lisa's surrogate dad and that's how he'd be brought into the fold.
if you joined the 4th you and unohana would probably end up being the most terrifying couple in soul society. (And zaraki would probably end up joining your faction).
anyways feel free to drop any questions. I'll be writing up a post mortem.