Guys who are talking about "valve make your own payment processor" just have no idea what are they talking about.
1. You can't just instantly create your payment processor or card service provider. There are a lot of legal bureaucracy and paper work, you have to get many approvals from different legal institutions to make it.
2. This process is very expensive
3. You stuck in 2010, era of financial monopoly of banks is moving toward to it's end. Asking for new "independent" payment processor is completely inefficient and obsolete approach for solving this problem. And it leads to future problems with new payment processor. But...

The real solution is accepting payments in crypto. Considering the recent adoption of the GENIUS Act regulating stablecoins and paving the way for widespread cryptocurrency adoption, its relevance of crypto is higher then ever.

Why crypto? Because here, payment processor is a blockchain.
Blockchain NEVER asks you a stupid questions that should never be asked by payment processor:
1. It doesn't care who are you and to whom you sending funds
2. It never asks reason for sending funds
3. It has no interest in origin of funds being sent
4. It doesn't belongs to single person, group of people or mean group of shareholders. Blockchain simultaniously processed by millions of validators, that also could be anyone of you. The purpose of blockchain - nobody owns it, fair transactions for everyone without any exceptions.
This is what payment processor shoud be: Blind, impartial, efficient, unquestioning.

Valve always been known as a company who pushes industry forward, adopting new technologies. So I am certain, this should be the case.

Also blockchain currencies are region free and equally available worldwide. Everyone can buy it, sellt it, use it. It costs the same price everywhere.

I often buy games as a retail key from online stores (it's just usually cheaper than in steam), that usually always accept crypto. And yes, I am using crypto to pay for games sometimes.

And you might think. Oh.. but cryptocurrencies are always volatile. Their value changes like a sine wave weekly.
Yes, they are. But there are always stablecoins around. For example USDT. It's a token tied to USD 1:1 and price always remains like that. They are frequently used for longterm storing with minimal riscs and for online payments. They are frequently used everywhere, where crypto is a thing.

And no, it doesn't mean Steam also have to adopt NFT slop and garbage crypto games, no. Crypto isn't about that. It is just a payment method.

How to adopt crypto in steam? Very easy.
1. Instead of removing games requested to be removed by payment processor valve just removes an ability to pay for this games with bank cards, paypal etc. If such game presents in cart you can no longer pay for it like you did it before.
2. The only available way to pay for your cart with "restricted" games is to pay with crypto.

This is rough approximation of how it should be, but if Valve decides to make it a thing they definitely would design this process in details with layers and specialists.

As long as a game does not break the law, the developer must have the right to sell it, and we, the consumers, must have the right to buy it.