Not just that, people have already tried.
Visa and MC just say that using any OTHER payment processor to handle transactions like that will still result in them pulling service. If steam or itch made their own service or had itch.adult, visa and MC would just pull the plug anyway. Theyre a mafia. Circumvention isnt an option
You either REPLACE them entirely, or, you legally fight them.
You aint winning either way.
That's why I said "exclusively", whatever store-front/service-provider you'd make would have to run without VISA and MC at all.
Theoretically, that IS possible. The problem is access. For example, where I live, I have
no other options for Debit cards except VISA and MC. Nothing. Nil. Nada.
I've looked into Virtual Banks, y'know, stuff like the Revolut bank and others like it, and nothing I could reasonably access offers anything else other than VISA and MC. I searched for
months back when the dlsite mess originally started for a JCB provider, and there's
nothing. I also found that attempts from JCB to expand in the European sphere of influence where pushed back hard by, you guessed it, VISA and MC.
Basically, short of moving somewhere in Asia, which is not a realistic option for someone like me, I have
no options.
Services along the lines of PayPal exist, of course, but none of them have the same reach. There's that one thing in Brazil. There's others in Japan, China and the general Asian Sphere of influence... but none of those service people in Europe specifically, and even if they did, making a store-front completely independent of VISA, MC and PayPal would be insanely hard right now.
You'd also have a very limited user-base at the end of the day. At that point, might as well just apply censorship to your games and sell them on dlsite. That IS, theoretically, an option, as far as I'm aware. I don't think their service is restricted to Japan.