If I set up a purely static HTTP-only site in 1998, it would still work with today's browsers, more than 20 years later.
If I set up a purely static HTTPS-only site in 1998, and didn't follow the upgrade treadmill, it would have stopped working for modern browsers some time ago.
Irrelevant. Low traffic static website.
> at which point you cannot postpone the kernel update anymore because you need the new device drivers, etc. etc
Irrelevant as I didn't upgrade the hardware
>You also don't want to stop updating your HTTP server, CVEs get discovered quite frequently
it's a server for serving a single static page from 1998, nothing bad will happen if that machine is compromised, well, nothing worse that what could be done for not having HTTPs
Here's one: the server has a remote code execution vulnerability, which is exploited to gain root permissions, and your server is serving child porn. The cops are knocking on your door.
Granted, this isn't a pro-HTTPS argument, but you do need to keep your stuff updated, even if it is only a static site.
Of course, migrating to even a raspberry Pi would be a net performance and perf/watt improvement.