I've been doing that on a Mukluk forever. 26" wheelset in the winter, 29+ in the summer.
It handles just fine as a 29+. It's just got huge clearance around the tires. I use it for bikepacking and an alternative to my full suspension.
The major issue is fatbikes tend to have a much wider bottom bracket, which some people don't get along with.
But, if you aim for a fatbike that's built around 4" tires, those can have something much closer to a normal mountain bike.
I recommend doing a test ride.