As a post script from me on this (not new information as such), I can surmise from all my understanding that the 10 Metre law was introduced as some form of safety buffer for the player waiting to catch a ball. He knows he has at least a period of grace from a player who is not allowed within 10m proximity and most likely someone who he doesn't immediately have his eye on when he is looking up for the ball. As such we see an immediate penalty for what might end up as a dangerous play situation.
If he at least knows such player has to be brought onside at some point, by the kicker or an onside player coming from behind the kicker, it won't be a surprise to him and he will be better prepared or preparing for it as a fair contest.
I am happy to suggest that it is not something to be mixed up with what we have been considering here. We can set the 10m law aside (it was at least 10 most likely, I think we all agree).
The loitering law for me is there only to address a totally separate issue. It's not one of safety but specifically of fairness. I err on the side of guys not being lazy and hanging around when they should be taking steps to get onside or be made onside by their team.
I can see no indication in the laws requiring us to differentiate between completed rucks, where the offside line melts away, and kick aheads, where the offside line remains.
Of course then we see the laws on offside in general play do then go on to mention the opponent making you onside. I accept that. But the offside laws certainly go on to say, in 11.9, while you might be onside you should not be permitted to have gained from your action of loitering which, if you accept it as loitering, is what you were doing at the time you were made onside.