You're making a marketing argument, not a technical one. Trying to build a new Photoshop competitor from scratch is probably a losing proposition for a variety of reasons, regardless of how you run the project or structure the code.

However, there are a large class of problems out there which do require a huge chunk of software if you want to address them in any useful way. No matter what you do to reduce coupling between modules there is a certain level of irreducible complexity. For those cases you need to do a lot of up-front design work or you're going to end up with a huge mess. And no, refactoring is not the solution here.