This is a crazy story but I still think Keybase gives you a lot to defend here. You have to compromise all the accounts and change all the proves to actually be able to send valid messages to somebody else.
That is a tall order, even if you use the same email as a username everywhere. I use long random passwords and 2Fa on a number of the important accounts. I don't trust google and Facebook, but I trust them to have some interest in not letting accounts be compromised.
Also if somebody changes all the proves, they will all be new and a smart system should be able to detect this sort of stuff in the future.
That is a tall order, even if you use the same email as a username everywhere. I use long random passwords and 2Fa on a number of the important accounts. I don't trust google and Facebook, but I trust them to have some interest in not letting accounts be compromised.
Also if somebody changes all the proves, they will all be new and a smart system should be able to detect this sort of stuff in the future.