There is basically zero chance splinterlands would ever agree to become the market maker as they don't have the cash liquidity to payout all SPS if there were a run on it.
I don't think @elon777 was suggesting Splinterlands would need to be market maker on both sides. SPS can be sold on various markets, so SPL doesn't need to make both sides of the market - it could actually just capture a small markup on selling in-game, but not offer any redemption ability. However, there might be some KYC and anti-money-laundering reasons against directly selling the currency in-game.