preDH.. what’s the deal?

I’ve heard whispers and ideas floating around about a preDH format from Sheldon and others in the community. My group and I are always looking for ways to mix up our meta, and found the idea interesting.

But I can’t find anything specific about proposed rules or restrictions of the format. I saw something about cards being only from pre-commander product times and such. But does anyone have insight on the specifics? I’d love to give it a whirl!