Yaniv Erlich has been talking about the stability of the cost of sequencing for the last few years on Twitter. For what it’s worth, I think the stagnation is probably due to lack of competition. Illumina could surely move the price point further down through squeezing more efficiencies out of the process. In fact, they are surely squeezing more efficiencies out and profiting from that.
What is really striking though is how the period between the end of 2007 and to the beginning of 2010 was like something that we never saw before, and will never see again. Not uncoincidentally this is also when 23andMe also brought direct-to-consumer to a broader audience interested in health.