I haven't been following the TLS1.3 development. What is the current state of SNI encryption? Is it possible to encrypt the name of the host you're trying to connect to?
At the point where the last drafts of TLS 1.3 were shaping up, Eric (Rescorla)'s initial ideas for how to achieve eSNI had failed and the extant draft was only a problem statement. It basically said: Here is what eSNI needs to achieve in our opinion, we don't know how to do that
Between that point and when TLS 1.3 was published, several people brainstormed a proof of concept for how to actually make it work, which so far led to the draft you've linked.
The eSNI draft is defined as an extension to TLS 1.3 but - since the whole point is to deny snoopers information about who we're talking to - if we have to "fall back" to not doing eSNI because the server isn't compatible then we lost.
Cloudflare and Firefox devs cooperate to implement drafts of eSNI, so if you have a recent Firefox and a site which has opted into Cloudflare's trial of this feature, then it works for you, but the drafts definitely will change further and you should not go building anything based on this draft that you aren't able to support updating to future drafts or abandon altogether weeks or months from now.
> Cloudflare and Firefox devs cooperate to implement drafts of eSNI, so if you have a recent Firefox and a site which has opted into Cloudflare's trial of this feature, then it works for you, ...
Well, at least not yet with the latest release version of Firefox (v69). Tested with Cloudflare's own page for testing eSNI browser support (and TLS 1.3, DNSSEC & DoH). Firefox supports the other three but not eSNI, according to that page. Even the Dev channel (v71) has no support.
The link you posted is the right one, but it’s to the Internet-Draft. This is the step prior to becoming an RFC, where revisions are stored for everyone (including implementors) to use. So (for example) when you hear someone saying “I support TLS 1.3 Draft 8”, that means they support version 8 of the Internet-Draft.
Not sure what's the implementation status though.