You mention briefly at the top that ACH transfers were "tested for a short time", are they no longer an option? I was under the impression you could get payouts handled that way if you contacted support. I know you said you don't have a bank account, and I don't know anything about you (or even what country you're in), but I'll point out that most people in the U.S. do have bank accounts, including many minors (generally its a joint account with a parent or guardian but still). Your position seems to be that you want to sell things for money online, but you don't have any way of receiving funds electronically. It's not your fault that you're in this situation, but you should recognize that it's not an easy problem to solve.
As it states on the payment FAQ:
itch.io is not a bank, you should request your earnings from itch.io in a timely manner
I know very little about what legal issues may or may not exist with a wallet system like you propose, but certainly from a business/practical side I can see why Itch might be hesitant about implementing it. It would require them to hold funds indefinitely, shuffling them around between various developers' accounts (while still handling taxes and such) until someone finally paid them out. That's a pretty big ask, and Itch is a pretty small company.