I'm wholly onboard with this in theory but the basic economic principles don't make any sense. 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.
But let's say there can never be a run on it and it'll always be a slow trickle of people taking profits and/or exiting. Again, they have zero incentive to do this simply because then they are holding crypto which can only be redeemed through themselves and thus worthless.
Splinterlands growth is flat. They are not getting any big influxes of new credit purchases nor summoners spellbook fees. The amount of SPS redemptions would far outstrip new user income. Not to mention operating costs and salaries. You can't pay taxes, server costs, nor payroll with SPS.
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.