Has anyone had any experience with earth over SIPs? There have been some earth roof projects locally in Austin, but wondered if I should consider any special issues with SIPs in such capacity.

I have no experience with this issue. But my first reaction is to run and hide. I know that if you do it, you must use sheathing that will not be affected by moisture. No wood and no metal. No matter how well you waterproof the roof, moisture will eventually get through and sheathing deteriation will happen. As much as I like SIPS, I would not recommend them in this situation.
Wes.

Check out Cement SIP's ... I am considering them

cement won't help as water will penetrate it. It just doesn't rot like wood. I am thinking it might work best to create a modified roof and then put the earth on 4' sections above pallets so that they can be removed if necessary to address future roof issues. I wonder if the Chia company would be willing to sponsor a project!