There are mobile apps in development and the API is coming along.
Kbin is still just a prototype though, but it's moving along nicely.
My other feeling is that kbin is setting up to be like iCloud whereas lemmy is more akin to sftp.
I've no idea what that analogy even is, but I think the differences are mostly technical (PHP vs Rust) and UX.
Both implement AP a bit differently, but at the end of the day, they're still AP aggregators.
And that's ignoring the political issues around lemmy's codebase ofc.