Well right now there are only 5 filled positions out of the 7 total. Who do you think the other 2 are? My guess is that:
The first one is buggy (ok we all know he's a weakling,but he has a very powerful crew and was a member of the Roger Pirates and that's enough to be considered fearsome. Also the fact that he received a letter by the World Government the same way as Jinbe reinforces this theory)
The other one must be a supernova. Well let's see:
Luffy, Zoro, Kid, Killer, Hawkins and Apoo are not Shichibukai. Also Law is.
That leaves 4 of them:
1)Drake. I don't think that he is a Shichibukai as he once betrayed the Marines
2)Urouge. I think he is too week to become a Shichibukai.Moria is much stronger than him and yet,he was considered too week
3)Capone. He is a bastard, I don't think so.
4)Bonney.Yes that would be ok.Although she is not that strong,she has an ability that can be very useful to the WG.I think they would make her decrease the age of the Gorosei so that they won't have to change every Generation
Tell me your opinion