Im not the first here to say this but DDR4 isnt compatible with DDR3 Ram. Here are the comparisons.
DDR3
1.2–1.65 Volts
800 to 2133 MT/s
240-pin
Pin spacing is 1mm
Width is 1mm
Height is 30.35 mm
DDR4
1.05–1.2 Volts
2133–4266 MT/s
288-pin
Pin spacing is .85mm
Thickness is 1.2mm (to better accommodate more signal layers)
Height is 31.25 mm (to make signal routing easier)
On a different note, the topology is different. DDR4 doesn't use dual or quad channel anymore
DDR3
Dual Channel
Lane 1 ==== Ram Stick 1 ==== Ram Stick 2
=================================
Lane 2 ==== Ram Stick 3 ==== Ram Stick 4
Quad Channel
Lane 1 ==== Ram Stick 1
===================
Lane 2 ==== Ram Stick 2
===================
Lane 3 ==== Ram Stick 3
===================
Lane 4 ==== Ram Stick 4
In DDR4, Every Stick has its own independent lane meaning if the board has 2 slots, its dual channel, 4 slots, quad channel, 8 slots, Oct Channel.
Lastly, the more sticks you use on a DDR4 board, in theory, increases bandwidth for the ram vs DDR3 your limited to however many channels the board supports.
http://en.wikipedia.org/wiki/DDR4_SDRAM
Although I used wikipedia, I looked at the sources for what i mentioned to confirm them.
First generation DDR4 Ram is suppose to be released sometime next month or January if it gets pushed back. Most Likely no Non APU boards will offer support. Only APU boards offer native PCI-E 3.0 support anyway.