Missed someone out from your list
Chandler Prime.
Jim mentioned in the Dragoncon Q &A he will be in MM, Drakul sent him to the darkest time-line.
Chandler is an expert on history and time travel, so I expect he will be playing a Basil Exposition role, perhaps not powerful enough himself to get back, but then Harry can bring him back to the Prime timeline, which will have all sorts of ramifications, as I doubt he would see eye to eye with the White Council after experiencing a year in the darkest time-line. Indeed it may be I speculate that Chandler sets up Alt-Harry with Harry Prime to stop him and get home from what may be a decaying time-line, about to be erased by the White God before it falls to the Outsiders imperilling all of reality, a fate Harry has to avoid in the Prime timeline. Harry has connections to multiversal beings aware of their doppelgängers like Mab, and the Mother’s as well as beings like Mr Sunshine who exist across the Multiverse as a single entity. Put the two together and you have an exploration of the multiverse, the Outside and the Prime universes place guarding against the Outsiders as the best hope of winning this cycle.