That looks great! Someone also pointed me at tmux thumbs, which takes a more vimium approach to this. I've got to try both of these.

https://github.com/fcsonline/tmux-thumbs

asciinema demo here:

https://asciinema.org/a/232775?autoplay=1

extrakto is really a "killer" plugin. I'm starting to wish for an emacs plugin with similar functionality.