This idea could be taken further to get past the past the ugliness complaint. Imagine something takes Markdown from these and renders it only if verified. Someone could stand up a TLS-protected site (possibly protected with a letsencrypt.com cert to reduce cost) that conditionally renders (based on keybase verify) and potentially caches renders for performance.
Either way, this is neat and I'm excited to see what other ideas our creative crowd come up with in using Keybase.io's new file system feature.
Regarding ugliness - I started on a stylesheet, and then just decided that wasn't the point. I just wanted something quick to demonstrate this use of KBFS, and I'm not expecting (or desirous of) people to use it as a genuine service.
I've been working a bit on a blog for my own ramblings (some here may have tried the naked domain and noticed it 503s) - I'm now interested in doing that as the demo here but fixed to my account. (And uh.. with a stylesheet and stuff!)
As you noted, it would then seem sensible to do some caching - but I think this needs careful thought to not destroy the purpose and benefit of hosting posts on Keybase. I suppose it would have to display the cached copy, and then load from KBFS in the background anyway, to verify it (not only as untampered-with, but also as being still the latest version).
An even more impressive trick might be a TLS server with SNI running vhosts which could check that the content was signed by a keybase user with a DNS proof for controlling that same domain. That would allow custom domains based on DNS CNAMEs. Now I'm getting carried away though ;)