I think an issue to monetize this is that if you build a web app, you are going to have a way to send emails, and a "users" table. Implementing email login on

I think an issue to monetize this is that if you build a web app, you are going to have a way to send emails, and a "users" table. Implementing email login on top of that is probably as easy as integrating with an external service, without the risk and the concerns about leaking user emails.