Jack Balkin nails it in two posts [beating me by an hour] and in the process explains why both Josh Marshall and Atrios have less to worry about than they think: I'll quote the second (my italics):
"What's important is not how many cities actually go ahead and do this, but the fact that the idea has moved from the positively unthinkable to the positively thinkable. And what is more important is that elected officials and not courts are taking the lead. As I argue in the previous post, that is how constitutional change occurs." Yes.

I'm critical of Balkin on occasion, but his philosophy is the closest to my own of any legal blogger I've read. He's the only one who understands the full importance, the full moral weight of process. Structured argument, as a mediating force, as a buffer, is the only foundation for law in a democracy.