Well, the basic premise of the article is common sense. The memory needs to feed the processor instructions and data.
If the clock speed and number of cores increases at a faster rate than memory speed increases (assuming all the cores share memory) then at some point the memory can't keep up.
Whether or not 16 cores is the magic number, I don't know.
Your assuming a linear relationship between memory access and number of cores but the size of L2/L3 cache mitigates the problem to some degree. We already have chips with 12+ MB which is plenty of RAM to run windows 3.11. The real question is what type of workload do you have and how well does that play with the number of cores your using etc.