Thanks for answering!
You're right about cocos2d, it will clearly not be replaced, especially for those that want to make cross-platform stuff or that are good enough to tweak cocos2d code by themselves.
I am making games as a hobby, so no time for cross-platform stuff. The simplicity of the Sprite Kit physics engine and the 100% Objective-C argument is very appealing to me.
It is clear however that you have priorities, I didn't know anything about the kickstarter. I'll stick to cocos2d as long as I need skeletal animation. It would still be good to know if a Sprite Kit runtime is something you might consider in the future.