I disagree with the proposal as is. However, with building spirit, I’ll make some suggestions, consequence of some thoughts already posted in here.
(1)
I would prefer to define the sybil in terms of his malicious intent or his personal gains. In that case, change this:
actor that has direct control over registered human accounts that don’t represent them
For this:
actor in search of personal gain by controlling registered human accounts that do not represent them
(2)
I would explicitly add somewhere that “It is not allowed to control the keys of any other human. Any suspicion of it is cause for challenge/removal, for which you must present irrefutable evidence that it is an exceptional situation.”
(3)
I would remove the human child example:
For example, a human child cannot be registered if their parent (who, technically is the submitter) is controlling their private key.
In any case, as you mentioned, it is very difficult to prove this situation. I don’t think we’ll be more sybil resistance just with policy changes. But it’s good to start with clearer statements and some warnings, which the judges should then evaluate in each case.