Because this thing looks like it could fill the same need as ProRes while being simpler and open source. For the applications are you are talking about, the format cannot be ruined because it is an internal implementation detail, in the same way that the stb_* libraries can never be ruined. They are yours and everyone's for forever.

The GPs advice about recording color space is spot on. Why design a new container when there are tons of ones off the shelf ones. The collection of files inside a Zip is my goto.