Something like abstracting all the problems around running something like that and the implications in the real world. Think about each part and make it as permission-less and trustless as possible. For example, one of the main problems of BTCPayServer is holding a volatile asset/converting it to fiat, which almost everyone needs. This could be automatically hedged into a stablecoin through DEX, and it wouldn't be such a problem for the merchant to hold it (without volatility) or convert it to fiat as they need.