I guess over time the significant increase in number of daily downvotes will (at least for most authors) lead to nearly the same rewards as we now have.

The problem is that most people don't dare to downvote, anyway, because of fear of retaliation. (In the post My STEEM Vision. I wrote more about the problem.)

If downvotes will generate (additional) curation rewards in future I may create a new (peaceful, not retaliating) account just to downvote it regularly. :-)