I'll admit upfront that I have only skimmed the thread.
I'll start with a simplification, which makes the experiment easier to conduct: Just remove one of the "legs". Now we have a pretty simple setup: A twin-lead transmission line, shorted at the end, between a pulse generator and its load. Anyone arguing for the "can only light up after one light-second or more without violating causality" (<- which seems to be a popular stance outside EE forums) position should be OK with this, as there is still a light-second worth of wire between the bulb and the source.
How does that behave? If load impedance ~ transmission line impedance, then we'd expect half the output voltage near-instantly across the load, as the impedance across the transmission line is..well the impedance of the transmission line right up until the wavefront bounces off the short at the end and has returned (2x delay time). Then the impedance looking into the transmission line will jump to ~zero and full output voltage appears across the load.
With a coax this is really nice to demonstrate:
No delay:
Some ripples and other reflections going on, because Zsource=Zload=50 Ohm, but ze cable = 75 Ohm.
With a transmission line things get more wild.
A twin-lead transmission line with 1 meter spacing and a reasonable conductor thickness has an impedance of around 1 kOhm. So clearly you're not going to light up a 12 V car lamp with that.
I constructed a simple ~10 meter long ladder line with ~50 mm spacing (~600 Ohms impedance) and used the same 50 Ohm source and load as before:
Reflections galore. Some voltage across the load instantly as before, but I wouldn't count that as "lighting up".
With a 600 Ohm load, we're only seeing about ~35 % of the output voltage across the load. I'm somewhat sure that this is because my setup is grounded and a ladder line suspended ~70 cm above ground has a fairly significant impedance to ground. With a high-impedance load I'm getting close to 50 % output, suggesting to me that the common-mode / ground impedance is around 500-600 Ohm.
So clearly you need to do this in space.