He's not playing any more, retired last year, so could coach full time. It's a gamble, but I think it could actually work out well for them.
Unlikely though, they've said they're going for an experienced coach who has won trophies.
If I was a Steelers fan, I'd want someone new and fresh to the league. Just use the rest of this season to see what the league is about and try out different things, and then be fully prepared for next season. And give the Steelers fans something entertaining to go and watch, because they haven't been getting that recently.