Optimistic Paymaster

You could use UMA to build an optimistic paymaster compliant with EIP 4337 and other paymaster systems. The idea here is that a paymaster could be loaded up with ETH to pay gas on users’ behalf, while taking their fee in arbitrary ERC20 tokens. That would be passive liquidity. Meanwhile, active participants would report on the current ETH/ERC20 exchange rates, lock up ETH as a bond, and take a cut of the fees.

That would be better than using DEX prices, which limit you to ERC20s with deep enough liquidity to get a good on-chain price and cost more in gas to obtain. The active exchange rate bonder could update all of the exchange rates in a single call, and since they are bonding in ETH, which is also what the paymaster is paying out in gas, the passive liquidity providers are protected.