It's hard for me to view Stan Kasten's resignation - effective at season's end - as anything other than the first step toward his replacing Bud Selig as the next commissioner of baseball.
Stan's resume is ideal for the job: running two MLB teams, an NBA franchise and an NHL team - some simultaneously - and a law degree to boot. He's far more qualified for the position than the guy who currently holds the job.
As for who replaces him with the Nationals, I seriously doubt they go outside the organization. An outsider as club president would want to put his own stamp on the franchise, and the last thing this club needs is someone rearranging the furniture.
Stan's of an age that would allow him a long run as commissioner, and I can't think of another candidate - one who'd actually be willing to take the job - who'd be applauded on both sides of the aisle.