Yeah it's good interesting stuff to experiment with.
Don't all his "grounds" go to the same place ? Because unless he has some actual ground between the individual ground connections it's just the same as many others have done. A Meyl like arrangement. I ran motors, filament bulbs, LED banks and even fluro's from my setup "which was similar but I drove mine at full resonant frequency with a DC chopper on the transmitter primary'. also I used an Armstrong Oscillator variant. And even transferred power from one steel shed to another via a single wire laying on the ground. He should know the neon will come on if he holds it even close to the coil. so should a fluro.
If he tunes his output coil he will get a sine wave output from it if the transmitter is outputting an auto tuned sine wave. And the power to the load on the output can be regulated by de-tuning the output tank.