Thing is, it's self balancing. Return is liquidity/fees, so if people decide it's not worth it, returns go up until people decide it is.  
  
The other part is that hive engine is already powered by a 0% apy liquidity pool. It's called limit orders. These are the current incentive to leave assets in the market, and people obviously do respond to the incentive. "Market Making", which LPs are crypto's attempt to decentralize, is the incentive to "close the gap" between the buy and sell limits.  There are already groups working to add limits for uniswap, and those will increase functionality and liquidity, and hive engine would be simply doing it from the other direction. We can assume some of those limit orders are people playing the market, and they would rather just play both sides as a market maker.