Interesting, and you never know until you try I guess!
I wanted to race XC on my Cheltenham Pedersen and wound up getting Panaracer Smoke 45's to fit by indenting the chainstays with a steel bar and a hammer working over a wooden anvil of sorts (tree stump).
I had a Schwinn Broadway hybrid I liked riding, and one day tried putting 29x2.1's on the narrow factory rims, all went well!
My Huffy TR745 was my first aluminum mtb with 27.5" wheels, and I surprised myself by squeezing in 2.4's on i51mm fat-bike rims (taken from my Mongoose Hondo from K-mart).
