Yes, the goal of the gist is also to showcase how to ship lab extensions with conda.
There will be a guide available soon, currently tracked in https://github.com/jupyterlab/jupyterlab/issues/9118
In the meantime you might want to have a look at the 3.0 branch of the extension examples repo: https://github.com/jupyterlab/extension-examples/tree/3.0
Which have been updated to target the latest RCs.
Or even at the source for the python file extension, which is a rather simple extension: https://github.com/jtpio/jupyterlab-python-file
Normally upgrading should almost of running the upgrade script (thanks Steve for this!).