A few thoughts I jotted down as I was blueskying the idea of the perfect hackathon. 

Not an everyone-show-up-and-work-on-isolated-stuff thing. 

All projects would be related to some (possibly new) protocol or format.  

A mail list or some other form of workgroup leading up to the event.  

At some really nice and outdoorsy place, so we can go for walks and maybe swim. Fresh air is good for thinking. 

I like to sleep. Make it two days not one. Maybe three.  

No prizes or awards or judges. The reward will be the experience, and the collective work that's produced. The point of the hackathon is to work together. The only way we should compete at this event is to make the group brighter, happier and more productive. Happier is a big deal.  

I have a list of people I'd like to hack with, but I realized it would not be cool to publish it while I'm just blueskying this. 

No publicity but also no secrecy. Everything is on the record for attribution.