Cool, I agree no one should use PGP servers the way I described, but you never know what people are doing out there. To do things the proper way, as you described, is difficult in practice for lots of people.
To answer the question, the point isn't to get an (email address, GPG-key) mapping. It's to get a (public-internet-identity, GPG-key) mapping. People sometimes do this today in an adhoc manner (e.g. tweeting your GPG fingerprint). We want it to be checkable by user-friendly software.
I see. That MO makes a bit more sense then, though is it not then limited to just Keybase.io and will no longer work if something happens to this service? Or more importantly, is there a way to make this distributed?
If the site went away tomorrow, you'd still have keys in your GPG keychain. You'd also have a local cache of the server-side data relevant to you.
All public server-side data is available as a dump (https://keybase.io/__/api-docs/1.0#call-dump-all). Private data like encrypted public keys and password hashes we of course will keep under wraps.
We don't have immediate plans to make the system distributed, but if someone did it, we'd find it very cool. It's just too much for us to do right now.
To answer the question, the point isn't to get an (email address, GPG-key) mapping. It's to get a (public-internet-identity, GPG-key) mapping. People sometimes do this today in an adhoc manner (e.g. tweeting your GPG fingerprint). We want it to be checkable by user-friendly software.