I'm using i3 for a long time, the only feature I'm really missing is `bindsym j [class="google-chrome"] xdotool key Down` so I can make vi like key binding for every program that I use.
If you're still looking, I quite like XKeysnail (https://github.com/mooz/xkeysnail) for that, although it does occasionally get confused. It does seem like it's something a WM should be capable of though.