Recent AMD roadmaps did not show any support for DDR4 in the year 2015. The company explained this fact with its expectation for high DDR4 prices that will keep the memory from becoming mainstream. The company did the same thing back in the 2004-2006 time period when it did not implement DDR2 memory support until DDR2 prices reached very low points.
Now the latest AMD CPU roadmap shows a different picture. AMD will implement DDR4 support in its upcoming Toronto APUs and CPUs but the chips will also support DDR3 memory to ease adoption and a later memory migration. Thus users will be able to use the common DDR3 memory once they purchase such a CPU/APU and then upgrade to DDR4 when the right time comes. The future Toronto chips will offer four Excavator cores and support for PCI-E 3.0. The Toronto APUs will also enjoy an integrated GPU from the Volcanic Islands generation.
The reasons for this change are hidden in the fact that Toronto can also be used as a server chip and this is where support for DDR4 is needed. The new memory offers high-capacity modules, high clock speeds and greater memory bandwidth as well as lower power consumption, which are excellent characteristics for servers and server memory as a whole. In addition for people who want to build cheaper servers Toronto offers DDR3 memory support and a bit of flexibility, which is always nice.
According to the new AMD roadmap the first Toronto chips will arrive in 2015.
Source: AMD