While (I think we'd all agree that) predicting technology decades ahead is hard,
it is not impossible that a group of specialists, after a thorough discussion, could
get the prediction about right.
I linked you to the report of Bell Labs achieving 10Gbps over copper wire. Here is the link to them achieving 100 petabits per second over fiber in 2009:
http://www.alcatel-lucent.com/press/2009/001797 This transmission experiment involved sending the equivalent of 400 DVDs per second over 7,000 kilometers, roughly the distance between Paris and Chicago.
These are demonstrated capacities for these two mediums. The only limiting factors for achieving such rates for individual consumers are physical and economic considerations for building out the infrastructure. Nonetheless the technologies for achieving exponential increase in bandwidth over current offerings is proven. Achieving these rates in practice on a scale coinciding with historical exponential growth of 50% annually, which
does take into consideration economic and physical realities, seems well within reason. I'm sure telecommunications specialists would agree.