"they want the GPG-loving techies to evaluate their security and software."
"This has to launch to the public with bulletproof security."
How is merely using Keybase.io a security evaluation? It isn't. Security evaluation is all kinds of activities with specialized skill working on source, interfaces, debuggers and so on. You do that in parallel with testing of usability, performance, reliability, and so on. So, they need the security evaluations but also need users running it through paces for other reasons. They can and should do both.
"This isn't exactly a social network, you can't move fast and break stuff, and just push flaming builds and iterate."
Whose asking for that? I believe I said patient, filtered user-base that are clearly told it is a work in progress given to them for evaluation.
"I understand where you are coming from and I would like it if they rolled out quickly."
I'm not even asking for that. I'm just saying they need to seriously increase their user-base and with more non-technical, privacy-focused users. What input they're receiving before launch needs to be as diverse and representative of what they'll receive after launch. They can still cap the user count or be selective. Closed with 10,000+ person backlog or wide open in full production is a false dilemma. Heck, maybe even a room's worth of people from each likely demographic, skill level, target platform, and so on. Will help spot many issues coming from each before production.
"Not even everone on HN has keys I bet, so the public isn't as anxious as you or I might be ;)"
I should be clear that I'm not factoring in the general public at all: they'll continue using Facebook Messenger, etc for private communications because it's cool, convenient, cheap, whatever. I don't waste time trying to push privacy tech, esp key management, on the public any more past improvements to infrastructure or tools they already use. Strong security/privacy is and always was a niche. However, as Keybase's vision realizes, the niche is potentially larger than techies with GPG or stuff in keyservers: people who would use it if it was simpler & less technical at interface. So, I advocate they get more of that audience into their user-base for feedback.