The point of this is so that the user can't modify the site at all, despite what the proposal might say. Their goals and non-goals are contradictory.
Running this content in a container will not protect you. Just don't even try to adapt to it. Reject it completely.
They also don't want users to be able to use adblockers, that isn't all they're checking for. So this absolutely is the case. Their entire proposal is contradictory.