Very interesting proposal. I see a demand in what you suggest when it comes to monetizing your stake for liquid funds. There would be indeed instantly a market for that. However, I am not sure that an average investor would be more incentivized to buy Steem because of that in the first place and that is ultimately our goal. Also, as @ura-soul mentions, we would loose the account recovery function because hackers could sell our SP instantly. That would be a huge loss of functionality in my opinion. I can sleep easiers with such a security layer on my most precious crypto account.