@sgamer82:
I've been thinking. This arc gives us high odds that the Straw Hats may end up having to fight a Marine Admiral. Should this happen, and should the Straw Hats win, they will have once again given the World Government cause for alarm. There will likely be a rush to replace this admiral much like there was for Crocodile. This raises the question of "Who Would They Appoint?" and I think that, if possible, there's one very obvious choice which you may already have figured out by my thread's title.
Why would an Admiral lose his position because of that? It's not like the Admiral is doing anything illegal, he'd still be doing his duty. The three currently with that rank are known as the strongest fighting force of the Marines, it's not like getting beaten would make that person any weaker.
Besides, the only reason Crocodile lost his Shichibukai position is because public knowledge was made of his leadership of Baroque Works along with his possession of dancing powder which was found on a ship connected to the organization. The World Government didn't want to strip him of his title, they had to take Crocodile's position away. Why do you think Moria still has his Shichibukai position even though he was defeated by Luffy? Because it isn't going to become viable public knowledge.
Even with all the above I personally don't think the Strawhats are going to fight whichever Admiral arrives at Saobady Isle, but that's for another topic.
Who do we know who can fight with Luffy, is determined to capture Luffy, and is currently seeking a higher rank so he can move more freely?
The answer is, of course, our currently-Commodore Smoker. If the Navy needs a new Admrial in a hurry, I could see him getting the job. Especially if they want that admiral to focus on the Straw Hats.
What are the odds, in your opinion, of Smoker getting promoted to Admiral if Luffy/the Straw Hats should defeat/eliminate a standing one?
I think Smoker would easily become a Vice-Admiral since he's actually trying to get promoted to get more leeway regarding where he can go. As I said earlier, I don't think beating an Admiral(which I already think isn't going to happen right now) would warrant whichever losing his position. I personally think becoming a Vice-Admiral would let him move freely enough to go after Luffy.
As for your last question, I obviously think there's no chance of getting promoted to Admiral.