Introducing Accelerated Mobile Links: Making the Mobile Web App-Quick
blog.cloudflare.com
blog.cloudflare.com
The main downside I can imagine is that the centralized gatekeeper (Google) won't treat the optimized content the way it treats AMP content today. But, we are locking ourselves into Google's solution if we let that stop us from exploring better alternatives.
AMP actually has a lot of really neat technical approaches to enabling rich content, based on open web standards. CPP seems like a nice tool for the toolbox, but it doesn't seem like a satisfying 1:1 alternative to AMP.