It's not fossilized, it's just that no one uses it. Put hot chicks on there or make it mandatory for logging into Slack and suddenly everyone will be using keybase.io, and honestly I think web of trust is a good idea and if a webapp can make it seem easy or intuitive then I'm all for it.
We're scratching our heads wondering why there's no forward motion when it's simply that no one is pushing it.
They haven't added or really changed anything since the acquisition AFAICT, it's just trucking along exactly as it was the day Zoom bought them out. Twitter account proofs were broken by the API changes years ago and nobody is at the wheel to fix or even just deprecate them.
We're scratching our heads wondering why there's no forward motion when it's simply that no one is pushing it.