Of course that's assuming a number of things, including that manufacturing costs, which are already very high for even single layer Blu-ray discs, come down significantly. The large amount of data per layer for Blu-ray increases the precision required to make them compared to DVD, resulting in a higher percentage of bad (unreadable) discs. It's reasonable to assume that putting 16 such layers on a single disc would lower yields even further.
There's certainly potential for adding just 2 or 3 more layers to accommodate increased resolution in future generations of HD video. At the same time, Blu-ray is limited by more than just storage capacity. It only makes sense that even higher resolutions would also require higher data throughput to accomodate increased bitrates, just as DVD's 9.8Mbps was deemed insufficient for current generation HD video.
So for now it's certainly an interesting development, and perhaps even revolutionary, but don't make any plans to buy 400GB Blu-ray discs any time soon.