If the NSA is your adversary model, Keybase isn't for you. If the NSA is your adversary model, NO system involving any central servers is for you, unless they only act as a dumb relay. Since Keybase is also the provider of your proof that another party is who they claim to be, they will always be suspectable to a government adversary. If you want to be NSA-safe, you can't trust any third party companies code, and that just leaves you DOA.

tldr; this isn't for the NSA adversary model