Currently a user can add a link to a Google Plus artist site and it won't be edited/shortened in any way. Google Plus URLs have already been added to MusicBrainz in multiple different forms . Optimal link should contain contain only "https://plus.google.com/" + ID (for example https://plus.google.com/106298806748844369997). https for the reason that every Google Plus URL with http:// redirects to https:// anyway.
Also when adding Google Plus links, "social networking page" type should be automatically selected. Currently the type has to be set manually.