First of all that's pretty hard to say for sure
1) You would have to get the whole world in a agreement and pull money together which would probably be impossible, unless only contributing countries would benefit.
2) It is much more a strutual feat than it seems. Remember, you have to run material through sub zero lands, underwater, hot areas, and who knows what else. It's not an easy thing to do. NOT IMPOSSIBLE, just not easy at all.
3) Nuclear energy is created by cutting atoms in half. That's a **** load of energy. And there's a never ending supply. Why go to the lengths of surrounding the earth in wire when we still have this option. Ultimately we will prpobably be using an anti-matter machine that will generate even more power. It's just not logical to wrap the world in wire with all these other options still in place.
Pulsating DC does not really make sense. What you are describing is a rectified AC sinewave. A rectified sine-wave has a DC component, but it also has a strong second harmonic. (and other even harmonics). It is the energy in the harmonics (mostly the secondary harmonic) that can pass through a transformer. But, the DC component will cause the transformer core to go into saturation and so the transformer will end up absorbing most of the energy in the harmonics.
A car's ignition coil works by storing energy inside a ignition coil's (inductor) magnetic field, which is proportional to the square of the current passing through the coil (inductor). When the circuit is broken, the inductor tries to maintain it's current, and generates a very high voltage to accomplish this. However, because the circuit is switched on and off, it is not true DC. A step in applied voltage (from switching the inductor) has AC content. This can be seen by looking at the fourier transform of a step function.