Maybe it can be done through Nostr. But Nostr is super niche and we deal with thousands customers, not sure how many of them use Nostr. If it is 1% it is a lot. I don't see email login as a big issue since you can use aliases etc. No personal information needed. If it comes to privacy the payment method is much more important. We prefer Monero for that reason. Best for us and customers. And with Nostr you have an identity as well, so it is similar to an email - identity wise.