Morning @inspector71 , thanks for your interest. All the addons, though they complain that they aren't compatible, should work fine. There are no new versions of the add ons than what Komodo finds on our server.
We are not planning on moving the Komodo code base away from XUL.
For editing add ons or writing your own, you can rely mostly on Komodo's SDK https://docs.activestate.com/komodo/12/sdk/api/. We wrap any Mozilla SDKs where needed/convenient.