Container tabs has that feature built in, you can say that google.com and youtube.com always automatically should open in the same container.

It's still too difficult and cumbersome to use. I might want to have one tab with gmail signed in but another to make anonymous searches on Google, both are on google domains so i have to manually fiddle with the containers again. Then you click a link in an email or search result and you don't really know if this tab should be in the mail-container, in the default container or in the domain-matched container.

I know that feature is there, I was thinking that there could be a maintained list of domain groups you could subscribe to like filterlists. That way you wouldn't have to wait for a Facebook Container addon and a Google Container addon &c.