Sense? LOTS of single track riders use backpacks. The banging a jolting of many packs is damaging and not sustainable. Each to their own. Backpacks are quite common. I use triangle packs well padded.Now we're talking, this makes sense. On top of existing current battery. Which one to choose is my next question.
Another reason I like flat foot frames, the longer wheelbase seems to mitigate the weight and balance. IME.Carry the spare as low to the ground as possible to keep the bikes center of gravity low. It's hard to beat the pannier option in this respect.