I gave a talk at QCon NYC in June about doing exactly this on a very large legacy system with over 400 developers. A blog post about it will be out on InfoQ soon. Replace process with engineering. Use DDD to identify the business sub-domains. Throw away project teams and organize product teams around those sub-domains aligned to the desired system architecture. Align teams with APIs instead of release trains.

Descale to scale. There is a ton of information on this out there from people who’ve done it, including me.