@Deicide:
I think there's two different possibilities:
a) Luffy and Blackbeard fight on Laugh Tale. Strawhats win on 1v1 fights and become the strongest pirate crew in the world, with Luffy as Pirate King. With no other threats to care about, the World Government decides enough is enough and the final arc is it sending everything it has against the Strawhats, with the Grand Fleet, allied kingdoms, Minks, Fishmen and everyone else rallying to joining for a big final war. This is the "War against the Gods", with Im as final villain.
b) Strawhats and their allies fight the Celestials and the World Government and crush the Admirals in the big incident hinted at the end of Dressrosa. The Revolutionaries top the current order and a new World Government, without Celestial Dragons. The marines are now on the side of good but are too weakened. Blackbeard becomes the greatest threat in the world, so it's everyone against him, ending with a big series of 1v1 fights in Laugh Tale. Luffy becomes the Pirate King in the end of the series.
I can't decide which one is more likely right now. I think that next saga is against the Celestial Dragons/CP0/secrets of the WG, but it could lead to either scenario.
Both your options seem like pretty logical ways to predict the future and your b is not something I really considered. I like it a lot!
Though I'm still partial to the idea of a full on 3 way world war with each group commanding an ancient weapon. Government/Marines, Black Beards, Straw Hats. With your ideas I never thought of the Admirals being challenged and potentially bested before the very end of the series though. That seems like a pretty good solution to the problem I always had in my head. The problem being that the Admirals were powerful enough to be final enemies to the Straw Hats but having them around and the Black Beards just seems like too much even for the Straw Hats.
There was a theory brought up here and there about Sabo defeating Akainu for good and it makes sense to me thematically(ugh please everyone don't pick up that word! It's the first I've used it in ages!) but my heart says no it needs to be Luffy! What if it's both?
Government Saga - Sabo, Vivi and possibly Hancock in trouble. The Grand Fleet can fulfill the narrators teases. Celestial Dragons, Tiger's Infiltration fleshed out. Kuma, Vegapunk and Bonney. All things teased fairly recently which in One Piece years is the last 10 years. Maybe Eneru's moon adventures and Urouge become prominent as well.
How ever this gets sorted out I'm starting to envision the Admirals being challenged by the Straw Hats.
Luffy Vs Akainu
Zoro Vs Fujitora
Sanji VS Kizaru
Jimbei VS Ryokugyu
I'm not too concerned about the match ups aside from Luffy vs Akainu but Fujitora as the blind swordsmen for Zoro and Kizaru and his yellow light speed kicks seem like a fit for Sanji. Ryokugyu does seem to have some personality quirks that could clash with Sanji but I really don't care about this aspect right now.
Should they fight maybe Akainu doesn't get out right defeated? What if the Marines just end up severely weakened due to the confrontation? I don't know how I'd write that to keep it satisfying for the audience but they could still come into play later on in the story after the adventure to Laugh Tale. This battle could be the end of Im and the Celestial Dragons as we know them but Akainu stays in power and more or less keeps the status quo. This gives the Revoltionaries one final goal for the world war after Laugh Tale.
In this scenario Teach and his gang could rise to become the most powerful threats the world has ever seen. So should a 3-way war happen Luffy and the crew take on the biggest threats like usual while Sabo can go after Akainu. Ace and Sabo could get their revenge and of course Akainu would be the final wall for real freedom in the world. Even if Akainu suffers his absolute defeat by Sabo at least we won't feel absolutely cheated because we got a grand showcase with Luffy nearly doing it himself once before.
Edit: Oh right…
After Kaidou and Big Mom
Luffy - 3 Billion
Zoro - 700 - 1.1 Billion
Sanji - 666 - 1.0 Billion
Jimbei - 600 - 900 Million
After World Government Saga
Luffy - 4.5 Billion
Zoro - 1.8 Billion
Sanji - 1.6 Billion
Jimbei - 1.5 Billion
After Laugh Tale Saga into the final war.
Luffy - 5.6 Billion
Zoro - 2.5 Billion
Sanji - 2.3 Billion
Jimbei - 2 Billion
Pure BS but its fun right?