This is a good idea, the only thing I would add is making down voting anonymous, because when you down vote a post chances are the person you down voted will simply down vote your post as retaliation, I think most people will still not down vote posts even with this hybrid system, especially people with not much STEEM Power, because they will fear retaliation...

Not knowing who down voted your post would be much better because there would be no retaliation wars, unless of course that person wants to let you know in the comments.