It really all depends on what the "new age" is all about. It's apparently about the age of dreams ending and the strong will be triumphant. If Shanks goes by this definition of the "new age", then he's betting that Luffy will be on top.
Buggy and Shanks went they're separate ways on Gol D.'s execution. Who knows if they went after One Piece or not? It is a giant war zone in the grand line apparently in this "new world", so its been proven difficult to get after even if you know exactly where it is.
Also if there are people who know exactly where it is, they would've been interrogated or known more better.
That's why I believe in the finding true history to find one piece theory. Gol D. could've planned the whole thing so that One Piece has to be found like an ancient weapon, through the Ponyglyphs.
That way only a certain group of people could find it, and thus another reason why the World Government put a ban on reading it:so nobody can find One Piece declare themselves Pirate King and disrupt the balance they're worked so hard to achieve.
NOTE THIS:JUST BECAUSE THIS THEORY IS FOUND THE SAME WAY AS ANCIENT WEAPONS, THAT DOESN'T MEAN IT WILL BE AN ANCIENT WEAPON.
going back on my earlier post it'll give a chance for robin's loyalty to be tested if someone like Whitebeard offers her a chance to find it if she helps him find One Piece.