DDR4 support is CPU dependent.
Intel is first planning this with the Broadwell-EP and Broadwell-EX processors which may come out the end of this year. These are server or enthusiast processors and will be expensive.
First mainstream processor support will be Skylake, which we might see late next year.
DDR4 support will also require new motherboards to go with these processors.
Don't imagine though that you will see any great performance improvement with DDR4. Current processors are not being hampered by memory bandwidth available with DDR3.