If I had the time, and could dodge call ups, I'd like to do something like this:
Almas vs Gargano - Ciampa run in.
Almas vs Sullivan - Sullivan wins.
Sullivan vs Cole - Cole runs away/gets DQ'd to survive.
Sullivan vs *Filler*
Sullivan vs *Filler* 2
Sullivan vs Black - Black wins.
You can do Gargano again by playing up the last chance story. Zelina can heel it up by forcing it into the contract too, no more title matches in NXT. Ciampa runs in and takes victory from Gargano and re-starts that program.
Then I go to Sullivan 'cos I want a monster to be the title holder for a while as it's different. I want to give Cole a match here as I think it's a good way to keep the title off of him while still giving him the main event slot. To keep him busy during the Almas run you can do a looser leave town thing with Sanity, with Sanity debuting on the main roster post-'Mania.
Your filler challengers for Sullivan really just depend on other storylines. I think there's a story to tell with Strong being a challenger after Cole and also losing, leading to him joining Undisputed. Not exactly sure how to do it, but the end goal of that is Strong splitting from them and beating Cole on his way out of NXT. Dain would be a good challenger if he's still around for some reason, a returning McIntyre would work too as a one and done before a call up.
It's not realistic, as Cole is probably the correct guy to have the title to carry the show, but I still like it.