I never would have thought to add coffee! I add extra bananas to mine, both mashed and sliced into disks so you get some “chunkage”. It’s super tasty toasted with cream cheese.
It was a spur-of-the-moment thing. I had one cup left over in the thermos. When I was making the banana bread, I went “Heeeyyyy! Waitaminnit.”
You can’t taste it explicitly. It lends more of a subtly complex note. The aroma was really evident when it was baking.
Aside from the taste, I kinda like having caffeinated banana bread.