I am really excited about DDR4 coming down the line for quite a few reasons.
1) In mobile it is going to allow for super high densities with extremely low power, making 4GB of ram in a cell phone and 8GB in a tablet very possible. This will fix a lot of the multi-tasking and productivity issues that these devices suffer in. The performance of DDR4lp will probably be no faster than what we have today in low end desktops, but the power savings will allow for much better active-idle power use to vastly extend up-time on a charge.
2) DDR3 in the desktop space has seen horrible scaling from 800 to 1866, mostly due to Intel's memory controller architecture. Hopefully DDR4 will force them to rethink their architecture in order to gain the performance necessary to entice people to upgrade. Hardly anyone upgrades for added CPU horsepower anymore, these days upgrades are all about fixing system bottlenecks, be they in memory, SATA, PCIe, or USB. DDR3 has been a known bottleneck for quite some time, so hopefully DDR4 breaks that barrier.
3) DDR4 may (and I understand that this is wishful thinking) be fast enough to use as an extension for graphics memory. Next gen games and 4K monitors are going to dictate that high end GPUs have 8+GB of graphics memory... which would make these devices prohibitively expensive! The hope is that system memory would finally be fast enough, and that next gen controllers would be intelligent enough, to allow the GPU to have direct access to system memory as an extension to their own internal GDDR, which would allow next gen GPUs to continue to use 2-4GB of GDDR, while having fast access to the 8+GB that they really need. I only replace system memory with each core upgrade every 5-6 years, while I replace my GPU every 2-3 years. It is much more justifiable to buy a metric crap ton of system memory every 6 years than it would be to buy 8GB of very expensive GPU memory every 2.
Anywho, good to hear that DDR4 is coming down the pipe! Late 2014 it will make its way into high end desktops, 2015 will be right on track to upgrade my desktop, and then we will see it in phones within a year after that.