Dunno. It won't be for a few years yet anyway. There's no compelling reason to "upgrade" to DDR4 right now unless lower power consumption is important to you. The timings on the initial offerings are horrible too. It'll probably take a couple of years until the technology matures a bit to really see its benefits.
I was thinking "Dance Dance Revolution? Havn't heard that mentioned in years" Then I realized that I was on the PC board.
I have 16GB of DDR3, got a good deal. When I build my next computer in like 5 years, sure. --- lllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllll lllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllll