I don't think the Kidd-Hawkins-Apoo alliance will be able to take down Shanks.
Shanks' main crew (~8 or 9 people from what we've seen) were enough to stop the war. Hell, even Benn Beckmann himself was able to make Kizaru back off during the War of the Best.
Unless Kid, Hawkins, and Apoo are all at marine admiral strength level, I don't think they can take down Shanks, who's implied to be equal or greater than admiral level, as well as the rest of his crew who are probably all at admiral level.
I think their alliance will probably do some damage to Shanks' crew though, at least enough that Luffy will hear about it.
Also, for all of you that say Shanks has a small crew, we only ever see the core members. I'm pretty sure there are more people in his crew.
I'm also interested in what the Whitebeard (Phoenix??) Pirates are up to these days. Maybe Luffy will find them and they'll team up or something.
edit: Is Kaidou's epithet "Hundred Beast" or "Strongest Beast in the World"? I've seen it both ways.