What about going to a 29"+ frame instead a 29'er or fat bike. Kinda a middle ground, build your wheel around a rim that will take a smaller tire (2.25) and still take a 3.0 tire as well.
As much as fat bikes are amazing, I would pick the 29'er over the fat bike if you are commuting. Way better options for 700c tires if your riding 25 km + per day to work... Fat bike would be painfully slow in comparison