Along with other somewhat superficial criticism John Edwards has been handed is the fact that he lives in a very large house. I think he can kill multiple birds here by promising legislation that would limit the mortgage interest deductions for monster mansions. What constitutes a monster mansion is a gray area, but personally I would start phasing out the deduction for houses bigger than 4,000 square feet and eliminate it entirely for mansions over 6,000 square feet. I would also either eliminate the deduction for second homes, or add the footage of the second home to the first home for purposes of figuring out deductibility.
I'm sure this would more than pay for the $1 billion program that Edwards has called for to help homeowners hit by the mortgage crisis (no money figure given in the link, but I've seen it elsewhere). It would limit the extent that the mortgage tax deduction is skewed in favor of the wealthiest. It would reduce the incentives people have to buy environmentally-destructive mansions that are almost always located in sprawl areas. Finally, Edwards has special credibility in making this proposal since it would affect him directly, and at the same time it neutralizes the criticism over the issue, turning it around into something positive he can point to.
A politically-easier version of this is to apply the limitation only to new homes built after the legislation is enacted. It won't bring as many benefits, but would still be helpful in fighting the monster mansions afflicting the country.