Since you are a lawyer why don't you define legal possession and how that concept can be applied to bitcoin for starters.
It is certainly subject to debate. My argument would be that possession of the privacy key constitutes the ownership and right to access the value denoted in the blockchain ledger. That is the basic premise of Bitcoin, correct?
Really? So if I post my private key here then everyone that sees it on this forum owns the btc in that address? What about any btc that used to be there? Do they somehow become past owners of that as well?