One of the most important reason for the WG to have the Shichibukai is for their respective great strength to bolster up the Marine forces to combat the Yonko (looks at Buggy... well, at least that statement is ALMOST correct there... "-_-) The Marines by themselves could not handle a Yonko's assault, thus the need for the Shichibukai.
However, rumor goes that the new Fleet Admiral (FA) had been strengthening up the Marines since his promotion. To what extend is yet known but here's the question:
If the Marines are now several folds stronger post-TS and they now have individuals that rivals to those legendary reputations of Mihawk, Doflamingo (yes, I am aware he resigned not long ago) and the likes, will the WG eventually discard the Shichibukai because Marines now could take on a Yonko on their own accord?
On a separate discussion, the Shichibukai are, at the end of the day, still a pirate. They stand as a wildcard in the fight between Marines vs Yonko. Chances are there that the wildcard may turn against them one day (depending on who leads the fight against Marines). The question for discussion here will be:
Do you think the new FA could have foreseen / predicted the possibility of this betrayal and prepared for it?
Trying something new here. Usually when we pit two characters together for a fight, we will only decide who of the two wins. This method pushes the decision further to answer not only the question of "Who wins?" but also "The winner will win by how much margin over the loser?".
Picture it as a tug-o-war match, the stronger one will definitely pull the middle portion of the rope towards them, the further away the middle portion from the centre, indicating the winner is significantly stronger than the loser.
For instance, Luffy vs Gaimon, I'd give a 5 point towards Luffy, meaning Luffy will win it easy, no sweat.
Luffy vs Lucci, I'd give either a point or two only towards Luffy as we know Lucci was a formidable opponent and (I think) remains as Luffy's strongest single man fighter.
Akainu vs Aokiji, judging from what we know, I would give Akainu a slight point or two.
Luffy vs Mihawk (Marineford), I'd totally give Mihawk a full 5 points, Luffy have no chance at all!
Get the gist? Let's go...