Since Irsay all but promised Pagano would be the coach in 2017 yesterday. He also said the new GM will evaluate everything and ultimately determine the direction they go, so it doesn't make a lot of sense that they'd have designs on Shanahan before that guy is even hired.
I also don't see any actual Indy sources reporting the Shany rumor yet, so who knows? Could happen, but it sure looks to me like Irsay determined Grigson had to go because he and Pagano simply could not get along and he wants to give Pagano a shot now without the Grigson factor. Also, Colts players seem to hate Grigson, but love Pagano. If I had to bet, I'd bet Pagano gets 2017 to make it or break it.