@Strawhat:
You actually think Smoker will replace Aokiji? I very much doubt it. He isn't going to become an Admiral any time soon. Plus, it was never said that there must be only three Admirals each time, it can be less.
No, there were never any statement that there has to be exactly 3 admirals. But I'm sure u've noticed that Oda is using a Momotaro theme with the admirals (with the dog, bird, and monkey). So I'm assuming that it will be a constant theme.
As for Smoker's probability, if Oda sticks to the Momotaro theme, then there will be someone to take the mantle of Aokiji right?
Now, who can it be: Surely there is only 2 possibilities: someone we know, or someone we don't know. I'm not going to talk about the ones we don't know cause its a null point.
Secondly, to be an admiral, u'll have to be really strong. And usually, with power comes fame, from there we can deduce that it will be one of the big names in the marines.
Among those big names we have Smoker, Momonga, Onigumo, Dobberman, and a couple of other VA's (forgot their names). Of all those, Smoker got potential simply by having a Logia fruit. It wouldnt surprise me at all that in these 2 years he'll learn something about haki (its said that VA level guys can use it), and grow in ranks. Besides, color-wise, smoke can be identified with blue as well.
So there you have it. My Smoker >> Admiral theory