I am building my own Chromium-based browser with a similar concept called "bubbles" [0][1]. Not doing a show-hn on it until next week because I need to build another release but feel free to try it out (I recommend building over using the one in the releases area as a lot of bugs have been fixed in master).
Oh and for the commenter wanting Ctrl+T in the same container, a Ctrl+Shift+T in Doogie does open a child page in the same bubble.