So.. A whale could use their 'bonus' downvote power to downvote

No, a mechanism (a generous description since it is more of a half-baked concept than a true mechanism) as I describe would be a replacement for 'bonus' downvote power, not in addition to it.. Since downvotes and upvotes would both be (under the right conditions) rewarded, there would not be an imbalance the way there is now.

Both downvotes and upvotes are valuable work. The soundness of the system depends on payout being a good measure of value, not too high nor too low. Currently only upvotes are rewarded and downvotes are seen as a public service where the system may benefit but the person doing the downvoting is not recognized in any way for this service. That's a large part of why we see virtually no downvotes.

Anyway, I don't think this is worth a whole lot of discussion since it is nowhere near solid enough to be implemented any time soon.