You're going to love a dropper post, congrats.

The thing about running both 29 or 27.5 is you can't go down from a 29x2.6 to a 27.5x2.8 the bb drop is too much, only 27.5+ bikes can be tire sized up, not the other way around unfortunately. 29ers are geo designed with a 1.5-1.75" lower bb than 27.5+, you'd be hitting pedal strikes everywhere, with a tire up from 27.5+ to 29 you raise the bb but if you're a fatbiker (teehee, we rule) you would have no problem with the higher bb, most people wouldn't unless you're a racer and bikepackers would love it.

Full tin hat mode here, the bike industry realized people were buying 27.5+ bikes and getting a second 29er wheelset for summer, xc stuff instead of a second bike so they killed it off. I know it sounds nuts and it probably is, maybe ;/ but you are stuck with any 29er you get and I notice flip chips and sliding dropouts are going away too. Kona won't put sliding dropouts on the Big Honzo but the regular Honzo steel and DL 29er they do. I know bikepackers would flip shit for a Big Honzo with sliders and some braze-ons.