Point of discussion for your meeting: fixing this problem now is more cost effective than letting the app rot while his user base grows (compounding the problem

Point of discussion for your meeting: fixing this problem now is more cost effective than letting the app rot while his user base grows (compounding the problem). One way to ensure a quality refactoring is to do a couple tasks (ML and redesign) which both demonstrate power of the new architecture and also let you and he verify it. You could also sell some integration tests and site monitoring.