Hi all,
Ryan Walklin, the creator of CesiumKit - a Swift/Metal port of a subset of Cesium - wrote a fantastic deep technical guest blog post on porting the Cesium renderer from WebGL to Metal:
http://cesiumjs.org/2016/03/29/Cesium-Metal-Renderer-Design-for-Apple-Platforms/
The article also touches on some threading and SIMD improvements. This is really impressive and insightful work, especially for a part-time effort!
Patrick