This is sweet! When we made Chrome some of us (OK only me) were enamoured with an IE shell browser named iRider - it had tree style tabs and pinning, so was useful in very similar ways

IIRC one of the things they did well that could work here is batch control of tabs by dragging across them - you could click on a close or pin button, then drag vertically across other tabs to apply that action - it made handling the glut ever-spawning tabs very easy