He's built a brand playing a character. If he drops the character his current fanbase may drop him. I mean he's gonna get attention due to his name and who he's replacing but if it ain't broke don't fix it.Late Night show ratings are the highest they've been in years.
Also, you guys are underselling Colbert, dude has all the prerequisites to be a an elite Late Night host. 20 years + in the comedy game, he has had his own show for years and has done so much other stuff prior to the show. He has great timing, is intelligent, and he can engage and challenge the guests without putting off the audience. He will do very well.