In consulting, that’s called “after work”. Got to pump those billables
Honestly though, unless it’s a feature that is completely outside the domain of the application. If you have to re-write your entire app then your app was probably dog shit to begin with
Probably right for most big box stores or multibillion dollar businesses. But you would be surprised how thin the margins are for local grocery stores. That 3-5% in processing could be used to compete or undercut big box competitors that price in the credit/debit card fee.
I think with the right approach (small businesses first) it could see high adoption. Plus it would make it slightly more attractive in setting up shop in places that wouldn’t otherwise get any attention (ie, food deserts)