Google Messages should be added to the messaging panel in the sidebar along side WhatsApp, Messenger, etc. Currently the work around is enabling custom sidebar apps and adding the link to Google Messages. While it works, it is separate from the main messages section and doesn't work quite the same as the other integrated options. It was also a pain trying to find the work around.

I would kill for something like this for chat & threads on google with my Opera browser but as its integrated into gmail and such it would have some serious html scripting to isolate and anything and everything would break it I suspect... But its a good wish and if anyone can do it, its Opera!