CEO Arthur Hayes is calling it "the rebirth of the XBU series". Which is appropriate given that they have had a lot of trouble getting liquidity on those XBU contracts which tended to have longer expiration times.
The fees for taker orders will be 0.3% to balance out this rebate, and to compensate the exchange for the risk of insuring settlement with no DPE. The leverage is only 5x on XBU though so the risk of losses to the system is a lot lower as well, as long as the liquidity remains healthy.
It's nice to see this effort by BitMEX to attract more hedging activity rather than raw high leverage speculation. Futures serve multiple purposes and to use them purely as speculative instruments without allowing legitimate hedgers to get utility from them is missing out on a big part of the equation.
They've also had some pretty harsh socialized losses (DPEs) recently, and the XBU series have guaranteed settlement so you don't have socialized losses on them, hence the higher fee.
The contract is only a couple hours old but the liquidity is GREAT. The spread is only $0.01 (one cent) right now, so the negative fee is really incentivizing some liquidity provision in this orderbook. It helps that it's currently the only hedging contract they have offered right now too. Check out the orderbook: