This is totally different. They're not re-writing their application from scratch, but replacing a core component with a popular, well tested and widely support one.

Indeed it is -- GP only mentioned he didn't know any example of a large amount of code being thrown out, so I provided one.

They are ditching their UI toolkit and dev tools as well. It does look like a complete rewrite, maybe with copy&paste of some old features like gestures.

Thanks for the link, it's indeed a good read.