I can see a battle not unlike Marine Ford somewhere near the end with Luffy and his allies and WB's old crew and so on making a huge battle against the world government. And if this were to happen, chances are it would mean someone personal to SH Luffy would be in danger. Yes, I know it sounds a bit like a redo of the Save Ace arc, however it would make sense for a couple reasons:
1) "The last age is called whitebeard" - Whitebeard waged a battle of never-before-seen proportions against the World Government which trully showed his epicness even though he didn't really 'win'. So how does Luffy overcome the name of the former greatest pirates in the world? With Roger he just has to find One Piece and I am sure he will get a lot of acknowledgement for going where noone except for Roger has ever gone before. But whitebeard is probably the second greatest, and what better way to show how powerful (influence-wise) Luffy has become then to wage another war on a government stronghold for whatever reason, except have this battle be very obviously successful. I mean, Luffy makes A HELLA ALOT of allies so even without a huge personal crew, I can see him gathering an army for some huge event with companions from all former arcs.
2) "I'm not strong enough to protect anyone" - As repeditive as that is, there is nothing better as far as showing Luffy's strength having risen to the level he is satisfied with then showcasing the fact that now even the World Government which managed to steal one of the Legendary White Beard's Nakama and execute him cannot do the same for Luffy and his Nakama beause Luffy has risen just so damn further in the world then even whitebeard. And lets face it, being strong enough to stop his nakama getting hurt is almost like a secondary goal, just as big as finding One Piece, and this would be a great way to juxtapose it against the Ace event and show the difference.