Fiat payment networks are terrible. If all the separate payment networks (Zelle, PayPal, Cash app, Venmo, etc.) were interoperable with Lightning payments, it would remove barriers to payments between two people anywhere in the world. Another UX improvement would be digital US dollar currency (CBDC), but physical cash would become obsolete with that (along with any remaining financial freedom), so it's good to have alternatives like tradable commodities and Bitcoin.