How would you "end to end encrypt" an email going from Super Secure Provider A to Outlook or Gmail? The encryption stops the millisecond it leaves Provider A's servers.
Correction: you can send links to a website where the recipient can see the text you wrote using a password.
Nothing about that is "email" anymore. The same method can be used to make "password protected SMS" for example. Just send a link to a website and a password. Encryption!
What we need is actual public key encryption/signing support on mail services, but that's not going to happen ever.