First, if any coach was brought in mid-season, all they would do is tweak the existing O and D systems. They would not be able to bring in new coaches, because firing the entire staff would cause chaos. If there was a young, up and coming coach on the staff, then I could see it. Additionally, Jones could not hire any coach currently employed - so he's limited to the assorted talking heads or an interim coach. All of which are reasons to stay with Wade until the end of the season.
As for the off-season, I agree with RW. No way Jones trusts an unknown when he needs to fill the stadium for the next several years.
My first choice would be Gruden - he's still young enough and ornery enough to get the players attention, and they would be tougher, if nothing else. But Gruden can't manage QBs. He would not only need an experienced QB coach, but he would also need to be smart enough to pick one up himself - outside of the special teams coach, and Dat, I don't know if Gruden would hold over anyone else on the team, and those two only under pressure from Jones.
I thing Holmgren's going to Washington. The offense is in place, and the owner is willing to spend $$$, if unwisely. He can make do with a vet QB, draft a new guy and bring him up to speed quickly.
Dungy's not coaching again, and I get the feeling Cowher isn't, either. I think he enjoys the studio too much, and isn't too eager to get back into the rat race short of a huge contract; I'd question whether his heart would be in it.