Can't do any useful caching for a purposefully cache-busting website

it's not cache-busting, it's captive-portal busting. there's no reason it couldn't be cached on some service that charges less for bandwidth than AWS does.

Although yours is a valid reason, but I’ve had a colleague of mine who isn’t savvy enough to use this when they need to connect, but they told me they stopped using it because it would show them the page even though they haven’t connected yet because their browser cached the page somehow. I’ve adjusted by using a private/guest browsing mode to open this page but the cache busting cuts it easier for people who have no knowledge of caching.

Ctrl-shift-R solves that?

Only if you have a keyboard. If I'm on a captive portal, most likely I'm on my phone.

Read http://neverssl.com/changes

I'm pretty sure GitHub would require SSL, no?

Not on a custom domain--it's optional, and you have to have a CAA policy that will allow them to get an SSL cert for your domain and agree to allow them to do so. It's only required for github.io subdomains.

There's an option to enforce it.