I think that's the cost of high frequencies. Check DDR2 timings and compare it to DDR3 and you'll see the same pattern. If you'll wait until DDR4 reaches DDR3-level timings, you might have to wait for a looooooong time
Correct, DDR4 still offers better theoretical performance than DDR3 even with the higher timings. Some select kits may not, as DDR4 is still in the early stages of use. DDR3 went through the same transitional period, but most DDR4 kits will have better theoretical performance. How much that increase actual performance still needs to be investigated further, but we have already seen in tests that it performs at least as well as DDR3, while also consuming less power. DDR4 for mobile systems is really a no brainer. I'm actually some what tempted to upgrade from my laptop which still has plenty of performance (i7-3632QM + Nvidia GT 620) like I demonstrated in this article:
I'm not tempted to upgrade for more CPU performance at all, but a little bit for GPU performance, and I'm very tempted to do so for the net reduction in power consumption that comes from the combination of the 14nm CPU fabrication, more efficient Skylake architecture, lower power chipsets, lower-power consumption of the DDR4, and the increased efficiency of Nvidia's Maxwell GPUs. All of those things add together for a significant decrease in power consumption compared to a laptop that is only 3 years old.