We're talking about glorified M&Gs here. I think I was pretty clear. One placeholder (DW -- Disney Whatever) per family unit per M&G session is OK with me, since they all experience the M&G at the same time, in the same instance. If there are ten placeholders ahead of me, then I'm OK with ten family groups, for ten M&G instances, joining them. Not eleven, not twelve, not fifteen.
Shows (where there are "mass gathering" pre-show areas prior to auditorium entry) cannot be regulated once everyone's in the pre-show area, so again, line order doesn't matter so much.
For ride attractions, I still firmly believe families/groups/etc should enter the line TOGETHER. Ride attractions involve sequential spacing (seats, vehicles) with discrete guest capacity. Those should remain strictly FIFO as far as I'm concerned. I'm ambivalent about those leaving the line for bio breaks when necessary, but only after having actually been in line. Anything else is not fair to everyone else in line.
And yes, I'm OK with single-rider lines, to maximize ride capacity. My only caveat is that I expect CMs to enforce single riding from the single-rider line.
It (the line) ends where the last person in/on it is standing. I will share that data with those trying to pass me.