A little prediction...
Long term, if bitcoin users can't be taxed, governments will have no choice except to start charging absurd amounts for electricity. We have to pay for roads somehow.
This is an interesting idea on how governments could attack bitcoins, but you have to realize if governments push up the price of electricty just to punish bitcoin miners, they would be punishing everybody else in society. People would not like it, industry would become expensive, etc.. Its not viable.