I updated the metadata.json and added v40 to it, and it allowed me to activate the extension. The problem is it doesn't seem to activate after that. I have added the Vlans through the nm-connection-editor, but when I click them to activate them, the menu goes away and when i check again, it didn't activate the Vlan interface.
This would certainly be a very welcomed extension. Probablly the most important to me of all the ones I have added. I would be willing to help however I can. My background isn't in JS, so you would have to point me in the right direction. I looked through the code, but I am definitely not versed enough in Gnome to know what would have changed. Thought I would reachh out and see if you had it on your radar to update.