How would that be any different than general Internet e-commerce, where there is no landlord forcing everyone to use its services? It wouldn't, and nothing disastrous would happen.
It would be the same as browser based e-commerce: stolen credit card information, fraud transactions, leaks of credit card information due to non existing security
This is exactly what apple tried to prevent (snd is earning a shit ton money with it): manual credit card entry because except the big ones almost no one would be safe
For sure, I'm shuddering right now just thinking about all the software packages I've had installed on my linux box the past decade that have (or could have had) donation buttons that send me to their sketchy payment processors. Can't believe I trusted them!
Imagine a world where people buy things on a website let's name it Amazon
Or pay for online auctions using something very sketchy, something like a PayPal
Imagine paying online for cabs, food delivery, books or to rent a movie or a BnB on the other side of the World, to buy a flight, theater, museum ticket
What a wild wild west it would be, we will be fighting each other like crazy if it wasn't for Apple that saved us all from ourselves...
I shudder at the thought.
I very much categorize Epic's actions in the "unsafe" basket.