I am not using it, so I don't know how it works.
Does it work on a conventional installation? That is what most people use.
Dependencies need to work. It would be ideal if you could list programs, not extensions, then automatically include all dependencies when updating any program.
Ideally, include the idea from the first post. Download extensions to another directory, and copy them to the tce directory when shutting down. That would make it foolproof. Even if this was just another script, which the user needed to activate.
If you don't get dependencies working, you could download the selected extensions to another directory, but not move them to the tce directory until some time in the future after they are all downloaded.
Keep up the good work. You may finish up with something worthwhile.