It's already pretty harmonized in continental Europe. And some of the differences are handled by the plugs/sockets themselves (eg. Type F plugs with both ground contacts on the sides and a hole for Type E sockets).
And Denmark. A few years ago I was in Copenhagen and realized I had forgotten my mac charger somewhere. Went to some mac store and bought a charger that surprisingly had a monstrosity attached to it that resembled this:
With the exception of the UK the EU standard (2 prong) non-grounded plug should fit any socket within the EU and the grounded ones fit pretty much all of them with the exception of Italy/UK.
