It does work Took me a while to uncover but if you want to have working >> and << you need to check Android Lockscreen in Poweramp settings. When you uncheck it you will get some info about android 4.3+ track info handling which might somewhat explain why this happens (and of course then you will lose << >> again).
I've just recently upgraded my Samsung Galaxy Note 2 to KitKat and Poweramp doesn't react to long press on >> or << on my HS3000 headphones. Other players react correctly. On android 4.3 Poweramp was reacting without issues too. When will this be fixed?