HTTPS Web UI & API Support
HTTPS should be a an option in for the Web UI.
I personally use a NGINX proxy which gives it https transparently, but it should support it natively as well.
This would cover the https://server/api/ namespace also. External plugins will need to allow the user to configure https as an option, just like port.
This issue doesn't cover HTSP which would should have some form of encryption layer over WAN connections.