After watching the CB yesterday, i came up with the same chain of events that you did about the electrode moving when it hit each statinary one.
Also i had an idea for the new gap, what if the electrodes were made into acorn nuts (capnuts), and use a threaded rod through the disc and a tungsten capnut each side, i'm sure the new lathe could drill and thread, make a couple of flats on the sides for a wrench, and shape the dome while cutting off
(i have the process in my head how this works)
Capnuts would also allow some extra material (heatsinks) to be bolted under the electrodes, and no need for grubscrews that can work loose in the layers of the disc material
Another thing would be 4 stationary electrodes, but spaced in a way that 2 will arc, then the other 2 will arc, that should reduce the heat