I like the idea, but now VAR is out of the bag, it will be used in the EXACT SAME WAY, regardless of the determining factor. Is there “light” between the players? Is it light at the shoulders? Waist? Feet? Where should this light be measured?
If a forward is leaning forward and a defender is stood up, what if the top half shows light but not the bottom half?
For me, it should be front (most attacking) foot versus back (most defensive) foot.
Is the front foot of the attacker ahead of the rearmost foot part (usually heel, but could be toe if they are chasing back) of the defender? If there is overlap, ONSIDE, but if his WHOLE FOOT is ahead of the defenders foot, then he’s OFFSIDE!
VAR should be able to draw a 1 simple line BETWEEN them. If not, no offside!