As a content guy, I have a few serious concerns.
First, I think this would be repeating a very big mistake from the past: changing too many variables at once. If you changed all three of these at once, it would be impossible to gauge the impact of any one of them.
Second, the problem's outlined above involve the selfish use of upvotes at the expense of the success of the platform as a whole. Over my nearly three years here, I have not seen any evidence that would lead me to believe downvotes would be used in an unselfish way. In fact, all of the evidence points to the exact opposite. This problem is exacerbated by the fact that receiving (and I mean receiving not earning) a downvote creates a far worse user experience than simply not receiving an upvote. I think it is safe to say that a person earning a reward, seeing the reward and then having the reward taken away is far worse than simply never receiving the reward in the first place (and I am talking about feeling and emotion here, not logic). I am sure someone cashed a huge grant check to study that bit of common sense... but I'm not going to search for it.
Third, why the urgency to change this now? Why not see what communities and SMTs accomplish before adding in another variable?