New bullet point: Do search engines index the HTTPS version of a site?

[lgarron]

This is probably the simplest indicator of whether sites will land on a secure version of a website the first time (regardless of whether the browser supports HSTS preloading).

It's probably also correlated with e.g. most links on the internet pointing to the HTTPS version of the site.

[Disclaimer: I work for Google Chrome. However, I think it would make sense to look at all top search engines that users might use.]

[lgarron]

Relevant: canonical URLs (which sites can use to make sure the HTTPS version of a page is always indexed... even if they haven't turned on redirection yet).

[benjaminp]

That's an interesting idea. I don't really know how to compute that reliably, though. I also note that redirecting HTTP -> HTTPS is a pretty good indication of where users will get sent from search results (once the crawler gets to it anyway).