RE: Businesses will issue custom stablecoins: what this means for the banks

I don't think there's any such thing as miners revenue when it comes to Trump’s family stablecoin so the revenue you seem to be talking about is definitely from something else.

Given that the Trump family isn't exactly transparent with its world liberty project, there's no way to know.

Certainly stablecoins can be designed to have fees paid to the issuer with every transaction on-chain but I don't think that would be a good idea, so the primarily means of generating income would be through investment of reserves in treasuries.