When Robin is going to be rescued by the crew our favourite fictional pirate group is going to have the next problems:
-DoFlamingo and his "new age" that is similar to the pirate summit that Ace talked to Luffy. He and his abuse can have an arc.
-If the Buster Call isn´t destroyed and the Strawhat survive they are going to face a continuous persecution by the Navi.
-Jinbei and his mermaids.
For me things like Whitebeard-Shanks alliance, Shichibuchai and Admirals are beyond the next arc with the logic in mind.
Obviously the Shichibukai aren´t going to follow World Government direct command but we have another groups of 5, the Blackbeard Pirates that are following Luffy.
5 Vice-Admirals+5 Blackbeard Pirates, exactly 10 people and if we add that now with Franky the crew has 9 members, add 1 more and you get the 10 exact people for fight against the menace. What do you think about all this?