I had a thought on how to address this that attacks the problem from a different angle.

Since you're so involved in tackling this issue, I thought I'd bring it up for discussion, maybe we could refine the idea some.

"TraderCoins"

Coins that are mined by making successful trades for someone else with their capital.

So whoever comes up with the most successful strategy to beat down bots benefits from it, perhaps greatly.  Even if they don't have the funds to actually make the investments necessary themselves.

The way I picture it, there would be a profit sharing component involved as well, so if you made a successful trade for me and it made me a profit of 10 BTC, you would get 1 BTC and some TraderCoins.

Perhaps the TraderCoins are the only currency used to contract new traders, so prospective investors buy the coins on the open market, and then spend them to retain a trader for themselves.