@Foxy:
I still think you guys are looking into it way too deeply. One word isn't going to change my view on it.
How would other people fit in with Kizaru?
Akainu, Aokiji, and Kizaru only work when they are together or separate. They are all based on the Momotaro Legend, are all the same height, all have a face based on an actor, all have a specific color, all have Logias etc.
It wouldn't work if Kizaru was with other random guys that don't fit in with his theme. It would be awkward and not make sense, that's why the former Admirals are all split up, because they only look right when they are together or separate.
Also, it would be an ass-pull if Oda made a random character that is Admiral level, and it won't happen because this isn't Bleach.
Those two spots that Akainu and Aokiji left are going to Smoker and Coby in the future, how more obvious could that be?
To be fair to you, Foxy, I also had the same impression. If the Admiral spots were vacant, then Oda would be saving them for Smoker and Coby. However, Smoker and Coby don't fit the rest of the themes you mentioned. They don't fit into the Momotaro Legend, they would be different heights, only Kizaru would have the face of an actor, only Kizaru and Smoker would have a color theme (Yellow and White), and even that breaks the three primary color theme, and only Kizaru and Smoker would have a Logia, unless Coby decides to eat a Logia Devil Fruit. Also, Smoker and Coby would be pretty at odds with Kizaru's attitude, especially when it comes to Luffy.
However, to me, it seems rather obvious that Coby is just Garp: The Next Generation and will likely stop at Vice Admiral level, like his mentor. There is also no way in Hell that Akainu would promote the little snot who stopped him and was praised by Shanks during the War unless Kong ignored his authority. I can see Smoker as an Admiral, eventually, but I feel that, as of now, the Admiral positions are either filled or there no longer is a three Admiral limit.