I was thinking of doing this in Finland, but then you'd be a money transmitter and probably have to do KYC, which trashes the UX and defeats the purpose.
Setting up BTCPay Server or https://opennode.com for my favorite online stores might be a better way to make them accept bitcoin. Help them with bitcoin storage, exchange and accounting. The EU kindly doesn't yet require KYC from them.
What would be even more rad? Crawl online stores onto Shopstr, let users send orders that are paid in Cashu. Notify merchant of pending orders and let them redeem the nuts. User can reclaim the payment if merchant did not respond.