iPhone development on the new MacBook
You really need to make up your mind whether you want the latest and shiniest product, or whether you want a good development machine. Once you use Interface Builder, a 15" MBP is the smallest that is usable without an external monitor. And once you use an external monitor, you are connected to a desk, and the portability doesn't help much. 

The new MacBook is targeted at certain use cases. Serious software development isn't one of them.