Hi Glen, I'm trying to answer that particular legal issue in this section of the post: "But what about property rights and harm to property holders from a fork?"
As a specific issue, it has happened on Steem before. Steemit Inc create a fork (I think someone said recently it was HF9) that changed balances on accounts (actually on further reflection, I think they changed the keys on those accounts to keys owned by Steemit itself), after someone obtained the keys of many users due to a bug on the steemit.com web site and began moving the funds of those accounts to their own accounts.