The description sounds very pragmatic and seems to make it easier/possible to render vectors with different brightness and also possible to render adjacent pixel glow?!
Thats a great improvement and will give vector games a more vivid appearance.
Without any deeper knowledge of the MAME sources I probably fail to see the full effect of the proposal, however if I just go to the Vectrex hardware which I know fairly well
I believe it will be difficult to render the ghost vectors of the beam zeroing as mentioned previously, these are sometimes non-linear and I would guess that is caused by the vectrex decharging some capaci/induc-tance in the deflectors.
There are also some home brews that took the Vectrex hardware, no modifications except for the cartdridge, to the extreme:
Vectrex actually has a preferred fps of 30 refresh cycles per second and the BIOS has a function to zero the beam and wait for the next cycle. The reason is that the beam only lives for so long and lower fps will make the screen flicker. The demo above uses the blank interval to play music on the deflector circuitry with the beam off.
Chew on that for a while, maybe it is too much to expect of an emulator.