I have never worked on a large Web app that required an unmanageably large JavaScript code base. They were simply built with one due to 1. too much structural code, 2. cramming too much in one page, or 3. cramming too much in one site. All of these are mistakes of poor design and architecture and using require.js won't solve that problem.

My current project uses require and after several months of working with the legacy code, I have not been convinced that it has improved maintainability. I would not use it again if given the choice.