Both Dan DiDio and Jeanette Kahn were hired from outside the comics industry, so it wouldn't surprise me that this will be the tack Warners takes again.
It might be someone from young adult book publishing from Warner Books.
That would fit in with the other rumor that DC will be bringing in new writers from outside comics -- from TV and animation -- because they don't want to keep going back to the same limited talent pool.
In that regard, it would make sense that they get a fresh perspective in the top office.
I think for us as fans, it would be best so that the person they do hire doesn't come with any negative fan baggage. Better to have an unknown, so that we can focus on the characters and stories rather than the backstage drama.
However, if they DO hire from within the industry, I voted for Karen Berger, who besides fostering the comics that eventually became Vertigo, also edited lots of great superhero comics such as Legion of Super-Heroes (coming in at the tail end of Great Darkness) and George Perez's Wonder Woman revamp among others.