Most important feature (and not to hard to implement?) right now. As Hubert said, I want to test my site before pointing the DNS records to the new site.
This is really important. If we're moving a large site to GP, or building a secondary site, we need to set up, and test, SSL *before* making the server accessible from the outside.
It is not desirable to switch it, then hope for the best when we request an LE SSL certificate or any other SSL challenge.
Very much needed. As well as enable the Let's Encrypt SSL verification via DNS for Cloudflare for example via UI as well. This can now only be done manually and it's kinda hard for beginners.