+1 for the github repo, you could add the instructions to group the devices to either the readme which is conveniently displayed below the repo files or create a wiki page.
Keeping the process private will certainly hinder testing.
I was waiting for a similar addon since I always wanted to find a way to sync watched status between devices but the requirements to use the sql approach (same kodi version) and the fact that the db could break anytime sql server is updated is a no go for me.