Middle English still works too doesn't mean it's not a problem to try to use it for a new project. Everything has trade offs, both staying on the old AND moving to the new. At some point everyone does move and managing the size of that transitional tail well is part of running a business well. There is not a one stop answer to the problem of when to migrate to the new and stop using the old but "always bleeding edge" and "always what we started with" are unlikely answers for most places.