I'm quite excited to see what php-ng will bring. I've had a hobby project that hammered PHP on performance, even making me wonder if I shouldn't rewrite it in say python or java or whatever, but I gave hhvm a whirl and was literally blown away by the performance gain. Granted this performance bottleneck was a whole load of php logic, basically a tight loop running over millions of rows and keeping track of various lists. so really something that php is known to be bad at.
I can't wait to see how php-ng will perform.
Although I also want to look at Hack, the strong typing really appeals to me. Especially for writing robust services where you just want to be explicit all the time.
Either way I'm really liking the direction PHP is going in.