Stripe only partners with a merchant acquirer bank. To replace Visa/MC they'd also have to get into the card issuing side of things: get a bank or banks to issue "Stripe cards" and get merchants to start accepting them.
Yeah, that's not how it works. Banks that issue cards contract with intermediary card networks like Visa/MC, not POS system vendors.
> integrating bitcoin lightning network soon
Been hearing that for years. Basic problem is while merchants would love to have lower fees, consumers don't have a powerful incentive to switch off using cards. The usual argument is they would save ~2% on prices but there is actually evidence that this would't necessarily happen. When Australia regulated down processing fees, the savings were not passed onto consumers.