"1. All lights powered by AC flicker at the same frequency as the line (60 Hz in the US, 50 Hz in many other places)."

The power being delivered to the lights is in phase, certainly.

The problem is the persistence of the ionization in the tube. It stays hot and bright for longer than 1/60th of a second. As a result the light output wouldn't drop to zero (or a significant amount) between peak current.

I'll bet that there is a component of the intensity that is modulated but I don't think it would be over 10%. I also would be happy to be wrong here.

Now, when they start making LED street lamps or using R.L.'s solid state orange laser to light the streets, then you're in business.