Just curious, but what's so awesome about fanless? If it's about noise, you hardly ever hear the fan on a modern Macbook/pro anyway. Definitely not unless it's being stressed. When you do hear the fan, it's reassuring to know the fan is doing its job. With fanless we might encounter throttling or greater heat issues, especially in earlier revisions.
I have ARM Samsung Chromebook that is fanless. The nice thing about fanless is that I never have to worry about blocking the fan vents and the machine overheating. E.g. I can have it sitting on my bed in a heap of blankets and it doesn't matter. Not the case with Intel MacBooks, and I generally use a lapdesk under my MacBooks to prevent fan vent blockage. Not as much of an issue with the rMBP, though, but it still can be.
That said, at least currently, I don't think a fanless laptop could be powerful enough to do what I would use a MacBook for.