i think the main assumption that keybase makes is an important one: you don't need to link a key to a person, you need to link it to an identity. and a github

i think the main assumption that keybase makes is an important one: you don't need to link a key to a person, you need to link it to an identity. and a github page or a twitter account is an identity. the IRL identity of the person controlling that web identity can be considered out of scope. if you do need to link a key to an actual non-digital person, then you've got a whole different set of problems.