I already did one of these, but I have a different idea regarding the time period that he goes to than the last one. Instead of going to a time period in which Kaien Shiba is still alive, he will be going to a time period that is shortly before the first part of the Thousand Year Blood War; the part that once over Yamamoto thought the war was done, in other words.
After the end of TYBW, Yhwach has been successfully defeated by Ichigo, however, too many lives were lost in the process, so Kisuke builds a time machine. I want Ichigo to reveal his powers immediately and become a captain; you might have to substitute OC's, as much as I hate them, for other captains and lieutenants and such. If you don't want to do that, just say that the Gotei 13 is still in it's earlier stages and only has some captains like Shunsui or Ukitake. Unohana might not be a healer just yet, so that'd be interesting to see. If someone can, I really need to know how far away the Gotei 13's foundation was from the first part of the Thousand Year Blood War, so that I can make this more accurate. Anyway, my request, in more detail, basically goes like this: have Ichigo try to peacefully solve the negotiations with the quincies rather than them fighting each other, and have Central 46's corruption be something that he and other shinigami work to fight against. After the negotiations are dealt with, Yhwach helps to train Ichigo's quincy abilities as a reward to him for the negotiations going smoothly. Ichigo's inner world already has a Yhwach, so he'll help the training as well. Yamamoto sees his potential too, and asks him if he wants to be appointed as the next head captain, and so Ichigo begins to train under him. Of course, he already is incredibly strong due to the events of TYBW, so what he really needs is to learn from Yamamoto in how to command people and the customs of soul society.
Several years (centuries?) later, when Aizen, Tosen, and Gin come into play, the Gotei 13 ensure that they keep tabs on them, defeat them, and move on. Gin will be spared punishment since his reasons were more justifiable, and he is technically on soul society's side. Even more years later, when all of Ichigo's friends in Karakura are alive and at the same ages they were before the wars, Ichigo reconnects with them all. This also goes for any shinigami that he was friends with, like Kisuke or Rukia. Yamamoto retired around this same time, and Ichigo becomes the new head captain. He establishes relations with the hollows in hueco mundo that he was acquaintances or friends with, and Zangetsu helps to forge these connections. This can all perhaps be covered in an epilogue or something. I don't really want the idea to end there, though, so perhaps this can lead into a crossover with DxD afterwards.