I realize this is currently a fantasy but would it ever be feasible or are there technical limitations preventing this from ever occurring?
The most obvious issue that springs to mind is the difference in voltage supplied from country to country. In the US it's 110V, elsewhere it's usually 220V or 240V. So I suppose replacing every electrical appliance inside, or outside, the US isn't a "technical" limitation, but it's certainly a limitation of some kind.
That aside there are losses when electricity is "moved" - they further you move it the more you lose. (that's a simplification, but it'll do.)
Politically of course, there are limitations as well. Assuming the grid was mostly on land, each country becomes vulnerable to another country cutting it off. I'm not sure that the US for example would want to be dependent on Canada, or Russia, and I suspect the rest of South America may not like being vulnerable to Panama, and so on.
Most of the generation would probably occur in desert regions, and I'm thinking that's already a problem with an oil based economy.
https://secure.wikimedia.org/wikipedia/en/wiki/File:Power_Gr...
Half of the country operates at 50Hz and the other half at 60Hz:
"In Japan, the western part of the country (Kyoto and west) uses 60 Hz and the eastern part (Tokyo and east) uses 50 Hz. This originates in the first purchases of generators from AEG in 1895, installed for Tokyo, and General Electric in 1896, installed in Osaka. The boundary between the two regions contains four back-to-back HVDC substations which convert the frequency; these are Shin Shinano, Sakuma Dam, Minami-Fukumitsu, and the Higashi-Shimizu Frequency Converter."
http://www.npr.org/2011/03/24/134828205/a-country-divided-ja...
You've got the best chance if you do something like this. No wires = no evil countries cutting wires.