we need a separate downvote rewards pool to encourage effective protection of the rewards pool

The incentives are already good enough. All shareholders already understands that this is in their best interest to protect Steem blockchain from spam and abuse.

The problem is not with lack of incentives, but with to strong disincentives.

People are afraid of revenge when it comes to flagging. This is simple as that. Therefore we need a way, to allow them flag content responsibly without a fear of being flagged-back

That is not a primary goal of my upcomming project "Wise" ^{_{(code name: SmartVotes)}}, but it will also allow stronger accounts, to delegate flagging and delegate decision making to smaller accounts.

I think this may cause that owners of smaller accounts will become a little bit more brave.

More details about the project... soon :)