[twr]

Proprietary? The backend maybe, but the keybase clients are open source. Some of the code is a little rough, and completed API docs would be nice, especially concerning KBFS, which is still missing. It's still under heavy development though, so these shortcomings should be understandable. (I personally won't use it much until I can actually develop my own non-reverse-engineered client, but that's just my requirement.)

I'm guessing you meant non-decentralized?

[craftyguy]

No, the server implementation is proprietary. Therefore, it's a walled garden that relies entirely on them. Supporting federation would be going above/beyond just releasing the server implementation's source under a permissive license. As it stands today, you have no choice but to rely on their proprietary server implementation, since the clients are useless on their own.

[twr]

Considering the whole point of end-to-end encryption is to reduce or eliminate necessary trust in the middleman, this seems like a minor, but still valid concern. Open sourcing the backend code wouldn't allow you to attest to what's running on the server. If the clients also allowed you to point to a custom server URL, which I would support, then the source availability might matter.