I thought of 2 more things I'd like to see that'll never happen. Once again they involve Arrancar and Visored.
1. Secret Task Force made up of the Visored (minus Ichigo of course).
2. Arrancar Division.
Of course like I said these two things will never come about.
First off because of the strong Anti-Hollow viewpoint of the Shinigami anything Hollow related is strictly forbidden. The Visored still have Hollow powers so it's unlikely they'd be allowed back into the Soul Society much less reinstated even though they were a tremendous asset against Aizen and his forces.
And while Arrancar are special and unique beings they're still technically Hollows so I doubt the Soul Society would want anything to do with them. Plus most Hollows/Arrancar have immense pride and an equally immense hatred for Shinigami so I doubt they'd willingly work with the Shinigami. And even in the slim chance there could be cooperation between the two it's unlikely there are enough Arrancar to fill an entire Division. And if there were exactly how would the ranking system work? Another problem is there is no definitive proof that Arrancar can purify Hollows with their "Zanpakutos" so the best they could do is stall the Hollows until the Shinigami get there. Much like the proposed Quincy Plan.
Still, as unlikely (even absurd) as these ideas are I still think they'd be an interesting addition to the story.