Memory standards tend to stick around for a long time. The DDR3 RAM still supported by the memory controllers inside Intel's Kaby Lake CPUs first hit the scene all the way back in 2007, though the speeds have increased and the operating voltage and power consumption went down in the intervening years. A brisk three years after DDR4 hit the market, JEDEC has announced that it's working on a specification for DDR5 memory, and expects to publish the design standards sometime in 2018.
The organization says that DDR5 memory will offer double the bandwidth and density of DDR4 along with increased power efficiency. Given the trend of increasing core counts and the difficulty and expense of adding additional memory channels to motherboards, DIMM bandwidth seems set to become more important in the future.
The standards body is also working on a specification for NVDIMM-P, the next-generation of the NVDIMM standard for memory modules that retain their contents after power loss. The NVDIMM standard could face competition from Intel's datacenter Optane products. Optane offers much lower latencies than even the fastest NVMe storage, along with the same non-volatile operation.
For perspective, JEDEC first started talking about DDR3 in May 2005 and products started hitting the market in 2007. The pattern was similar for DDR4, whose final spec arrived in September 2012 and was supported by CPUs released in the second half of 2014. We would expect a lead time at least that long for the first DDR5 products. JEDEC says more information should be available at its Server Forum event in June.