I'd like to to know whats available or not in the leap sdk on linux.
For the most part, feature-complete.
We've documented some known issues like leapjs requiring a special setting for Chrome, hasFocus() functions not supported, and occasional hangs on application exit.
The Linux SDK comes with a README that covers other various caveats.
Is the diagnostic visualizer available?
Yes.
are there major things I'd be missing on linux?
App Home, primarily. We don't have any plans to support App Home on Linux.
Orientation (Playground) was missing for a time, but we added that in with V2.