If we were willing to accept SSDs being as unreliable as human memory, we could increase capacities by an order of magnitude with current technology. In fact, if SSD controller design weren't so tricky, someone would have taken advantage of this already to build a pretty decent enterprise-scale caching system.
>being as unreliable as human memory,
That's actually considered to be a feature. http://en.wikipedia.org/wiki/Hyperthymesia
And given that nature has managed to cram this amazing sentient device into a space the size of our skull, using a pretty inefficient design process, I'd say the problem will be not the quantity of the building blocks, but how they're organized :)