> Beyond deploying service workers and hoping those struggling to bridge the digital divide make it across, I don’t really have a solution here.
One way to get around this would be a MITM HTTPS certificate, which would allow a local caching proxy to decrypt and encrypt requests. This means you'd have to install the certificate on each device you wish to be compatible with the caching proxy (otherwise it can't decrypt it), though.
See also https://meyerweb.com/eric/thoughts/2018/08/07/securing-sites... - which points out that when every site moved to https it broke local caching proxies, which had a big negative impact on people in countries with slower internet.