I'm really happy to hear about the Entity API being on the roadmap for 2015. It is something that I really bave been missing building applications with Cesium.
I would like to suggest a few things I find missing in the current API.
1.Why should an entity be composed from only a single primitive of each type? I have several use cases in my app where I need to compose an entity from several billboards and labels. I would like to suggest making the primitives that compose an entity a bit more generic. Something like entity.addPrimitive or whatever.
2. I would like to compose entites out of smaller entities making my entities more component like.
What do you guys think?