Bill Murray recently made an appearance on The Late Show and while there Letterman asked him about Ghostbusters 3. Murray sorta said that he's kinda into it (and it seems like it's actually happening), but then they discussed the rumor floating around about an all-female cast. "I think it would be swell. I would go watch that one in a second." Murray says.
They then go on to ruminate which female actresses could be in it: Emma Stone, Linda Cardellini, the female cast of Parks and Recreations, then the audience gets involved and someone, some genius, shouts out "Betty White!". Game over, that guy just won.
After sorting out the cast for the next Ghostbusters and in the middle of talking about new film St. Vincent, which sees Murray covering Bob Dylan, Murray goes all Bill Murray and remembers he made a promise to himself to run the New York marathon.
He then promptly gets up and leaves the studio to go train for it on the streets of New York, while wearing his tuxedo. Run Bill, run.