The biggest pain for me (in charge of building the WCSD15 site) was the Jetpack CSS/LESS editor. Sooo painful. I felt like it was trying to build a site with handcuffs on. It would be GREAT to go beyond CSS with full fledged custom themes. Then we can really wow some folks with our WordCamp sites instead of a lot of the same layouts which tend to all look the same after awhile. I understand it's a security concern but surely there's ways to figure it out. I'm going to go fill out the survey now.