I have been working on a python module and command line tool for managing Gnome Extensions. The goal is that the tool should be able to install, remove, update, enable and disable extensions from the command line. I was able to this thank's to this blog post by Nicolas Bernaerts.
It is in development and does not have all features working yet. If you want to report a bug, submit a fix, submit a new feature or any kind of improvement, feel free to do that on the GitHub page.
Edit: All planned features should work now but it may still have bugs.
Fair enough, I called it that since I put it out without having tested it properly and since the main features (installing and updating) don't work yet.
Sorry, I pretty much put it out as soon as it sort of worked, wrote a quick README and went to bed so I could not help you to get it working. It is indeed not fair to assume that everyone knows how to install python packages. I've written instructions on how to run it and how to install the requirements on most popular distros.
This would be amazingly useful. Right now I have to open Firefox every time I want to install an extension just because I'm a lazy idiot, but I'd prefer a more apt-get style approach to extensions.
Just wanted to say (a day late) that the package has been renamed from GnomeGet to gnome_get to comply with proper python naming convention and that installing and updating now works. If you installed the package uninstall it with sudo pip3 uninstall GnomeGet and install it again with sudo pip3 install git+https://github.com/chmod000/GnomeGet.git. When you want to update the package, use: sudo pip3 install --upgrade git+https://github.com/chmod000/GnomeGet.git