Seriously! We were trying to build our video editor in the same style (eg like tinypng and GIF optimizers).

It's so cool to do it all in the browser!

I even built a simple landing page creator that let you change text and images, then created a zip file that you could extract to your web host - no backend needed!

I think for me, CORS is the biggest hindrance to some of my ideas, esp. around editing, creation, and working with the content.