I guess it's only a problem if you for some reason believe sha256 will not be commoditized. The fact that energy costs keep becoming an ever higher percentage of the price per Bitcoin instead of hardware seems like it won't be a problem.
The greater proportion of mining costs that are due to electricity, then the more exclusive mining becomes. Because there are a finite number of slots next to hydropower plants. Not to mention, that the powers-that-be in government can probably provide the electricity for free and charge it to the collective. Utilities are one of the highest regulated, collectivist corruptions on earth.
Edit: even heating your home with the miners is not profitable because heat generated from electricity is much more expensive than from carbon fuels. And even micro-hydropower won't reach the 2 - 4 cents cost of large scale hydropower unless you can amortize the construction and capital cost over several years:
http://www.rockyhydro.com/Generators.phpAnd that doesn't even include the cost of the land and the rarer locations where there is enough flow and head drop to make it worth while.