How can I make the new "Open Tooling" work with multi-app workspaces?

Assume that I run the following commands to create a new workspace and one application in it:
Code:
sencha generate workspace TestWorkspace
cd TestWorkspace
sencha -sdk /path/to/ext-6.6.0 generate app SenchaCmdApp SenchaCmdApp
If I then run "ext-gen upgrade" in the workspace folder, I get the error
Code:
no such file or directory, open 'app.json'
If I instead run "ext-gen upgrade" in the SenchaCmdApp application folder, I get the error
Code:
no such file or directory, lstat 'workspace.json'
From these error codes and from looking at the code for "ext-gen upgrade", it appears that "ext-gen upgrade" is not designed to handle multi-app workspaces.

I also tried to manually do the steps "ext-gen upgrade" was not able to perform and then run
Code:
npm install
npm start
Which results in
Code:
Error: ENOENT: no such file or directory, scandir './packages'
Have I missed some documentation for using "Open Tooling" with multi-app workspaces? And when/how can I replace the use of "Sencha Cmd Packages" with npm packages?