I've had an idea. The first arc, which entails the Jakakumei reaping revenge for the imprisonment of Nobunaga is the mainstay. The ending of the first arc would involve the Jakakumei finding and releasing Nobunaga, then with this insanely powerful new leader they are more or less told to join him in an overthrow of the Gotei 13.
The Jakakumei are reluctant at first but think, why not? They took and imprisoned our captain for no reason and he deserves his revenge. So there is a time in which the Jakakumei and Gotei are at war all over the Seireitei, but as the fighting continues the Jakakumei and more prominently Nobunagas old luitenant start to notice that the love they hold for their old captain isn't mutual. He continues to use them as pawns in the war and sacrifices them as soon as it is a profitable move. This really unsettles the Jakakumei, their captain isn't the great man they once knew right at the end of the arc the head of the jacks and past leuitenant of Nobunaga goes in secret to the Gotei in an attempt to reach an agreement.
So starts the second arc and now the Jacks have seen the truth they join forces with the Gotei to take down Nobunaga together.
Now I also had the idea that all through the first arc the Jacks actually contact some Arancar to try and gain their help to rescue Nobunaga and once the Jacks abandon their old Captain, nobunaga himself returns to those Arrancar and has them fight for him against the joint forces of the Gotei and Jacks, but that seems a little to much like Aizen to me has, ordering round a group of Arrancar against the Gotei.
But what do you all think about it?
P.S I've probably made. Shit ton of mistakes in this post, but you will have to forgive me I'm using my phone.