Let's encrypt integration
It would be great to integrate the ACME protocol in IIS. One of the reasons SSL isn't widely used is because it is complex and costly to set up.
What I would really like to see is in the "edit bindings" window, when choosing a certificate, an option to choose instead Let's Encrypt / ACME. IIS would automatically request the certificate through the ACME protocol and would automatically renew the certificate.
Obviously this would also be available through powershell (although keep in mind that primary users are likely to be unsophisticated GUI users, not sophisticated teams who run multiple instance and load balancers).
Let's Encrypt inegration through installation of a extension (similar to UrlRewrite) would be a great add-on for IIS.