IMO, 20,000 is already way to much, but when that reaches 100,000 even just editing it will be a chore, let alone using it. It will simply be unmaintainable and unusable. I say this having worked on code bases which have reached that point and attempted to deal with the issues it creates. There's a reason every decently sized code base out there uses multiple files and a hierarchy. It's a natural way to create modular code, and modular code is simply better code.