Rather than leaving all this to the many registrars, what about a SaaS (let’s call it usemycustomdomain) that allows you to point a CNAME record for a subdomain to it, then when you sign up to an app that supports custom domains, you can oAuth2 to usemycustomdomain. Then usemycustomdomain can do the SSL management and termination and proxy the traffic to different SaaS products. It could even support custom URLs on a domain.
That would make it more flexible, but in my mind the whole point of this thing existing is to take the pain out of having a custom domain, and making the process accessible to more people. Part of that would include handling registration and hiding all the DNS nonsense unless you really want to fiddle with it.
