I doubt he's interested, but I like the idea. And not because I think Miller would be "faithful" but because I think he'd make The Punisher cinematically relevant.
The biggest problem I see with The Punisher on film is that the armed urban vigilante has been mined to death on the big screen. It's no coincidence that The Punisher was created in the 1970s shortly after Death Wish. While The Punisher is a good contrast to the normal comic book heroes, the skull iconography is really the only unique thing he brings to the movies. What was the last urban vigilante movie that was a true hit?
I think the other main problem is that the Italian Mafia isn't seen as a formidible foe any more. Goodfellas and The Sopranos have certainly deromanticized the Mafia and indicated that they survive as much on luck as on any special skill. Arguably, the Punisher's most favored foe is now largely considered irrelevant.
The face of crime for much of America now is black gangbangers and terrorists, specifically Osama Bin Laden. Is anyone crazy enough to make a movie about a white vigilante gunning down black gangbangers in this political climate? Does anyone in Hollywood have the chutzpah to send The Punisher after Osama Bin Laden? I don't even know if Miller would go there, but he'd certainly think of some hook to make The Punisher relevant again.