The main issue with Liquid would be the fees vs. the very small amounts people typically zap, but for larger amounts it would be viable. Ecash/cashu solutions sound promising but until there are mints and wallets with proven track records it’s hard for me to imagine using it for anything other than experimentation with tiny amounts. Lightning by itself still sucks for asynchronous payments unless you’re using custodians or have the ability, funds, and time to run all the necessary infrastructure yourself.