Here's my 2 cents based on zero inside information, just pure speculation:
As far as Gruden goes, I think everything comes down to the W-I-F-E. If the wife says she doesn't want him to coach anymore, he will stay fat and happy making 4 million in an announcers booth (my guess is this is not the situation though). If the wife says she wants to live in Knoxville, he will be at Tennessee regardless of what NFL team comes knocking. If the wife says she doesn't care, he's going to go with the best chance of success at the NFL level. Doesn't matter the history or tradition or how much he might win at UT, going to a team like Philadelphia is a better situation. Period. He will have a talented rookie QB (Nick Foles) that he can mold, a good RB, a couple good WRs, and a lot of talent on defense. There's no way he picks UT over that situation. If I had to guess which way he will go, I'm guessing the wife doesn't care and he goes to the NFL, but that's based on no insight just pure speculation. Right now though, it's realistic to speculate on Gruden coming to UT because there has not been a credible to rumor that says otherwise, but there is a connection with the wife which if you don't think is important than you're kidding yourself. I will be surprised if he's coaching in Knoxville, but I won't be shocked.
Realistically I think these are the coaches that are realistic options. By realistic I mean we're not going to pull Nick Saban from Bama or Chip Kelly from Oregon and probably not Chris Peterson from Boise.
Top Candidates:
Charlie Strong - Tons of SEC experience, strong defensive background, turned around an absolutely floundering program. Yeah it's the Big East which is not on the same level as the SEC, but a winner is a winner and so far Charlie Strong has been a winner. He's young, he's energetic and he get's the most out of his players.
Tommy Tubberville - I understand people don't want a retread, but SEC head coaching experience shouldn't be dismissed. His teams were always solid despite a couple down years, and his teams almost always perform well under the spotlight. He brings the name recognition also for recruits. Get a good staff under him and I think he could make UT relevant in a hurry again.
Bobby Petrino - Another guy with SEC experience and success. I think this guy could do exactly what he did at Arkansas in terms of building the program back up. Some people won't like it because of his character flaws, but they need to think about how badly they want to win...and win soon.
Up and Comer:
Butch Jones - He's had success at his 2 most recent schools. His players play hard for him and he simply gets results. Is he ready for the jump from the MAC to the Big East to the SEC? I don't know, but I wouldn't bet against the guy.
Wishful Thinking:
Gary Patterson - May not be realistic, but open the checkbook for him and see what happens. I love the way his teams play and I think it's exactly the kind of style that works in the SEC.