That is massively epic. I like your theory of Dragon having Luffy lead the Revolutionaries. If that's not what he has in store for him, he probably wants to help Luffy shake things up in the New World so that the world powers go out of whack, making his job as a Revolutionary, easier.
Now just replace the Redhairs with the pirates of ALL the Yonkou, and maybe a pirate crew of Giants for Usopp (assuming Ace is teh dead).
Now THAT is what I call 8000 followers!
EVERY FRIEND THAT THE STRAWHATS MADE WILL COME TO THEIR AID IN THE UTLIMATE BATTLE, EVERYONE USING LABOON AS A TRANSPORT!!!
the two giants, forgot their names, could go back to Little Garden, and then, after returning to their home, could lead an army of giants that will fight at the side of the Great Sogeking. There's also the army of Arabasta,
Even Chu-Chu could help, and Woop Slap! imagines Chuchu biting corrupt agents and Woop Slap smacking them with his staff
And yeah, surely the other Younkou may join forces with the Strawhats, or they crews could join them after their defeat their respective leaders, who knows what's Oda planning, but it would be awesome if every character, everything thing the Strawhats did, actually had an impact in the world, and what's a better form to show it than every person that they helped reuturning the favor by aiding them against Blackbeard, who's obviously has big plans for the future…
And what about Lucci? He even said that he would like to have a boss like Luffy. And Crocodile and Buggy could also help, specially Bon Clay and the other members of Baroque Works. But you know what would be hilarious, if Wapol created an army of toys to defend his future costumers, assuming that there would be a Mass Invasion of the Planet, perhaps Space Pirates will be involved with the creation of the Ultimate Weapons, or..
The Five Elder Stars are ALIENS who change of Form/Age to stay forever in the power! o_O
No, seriously, this whole "Ancient Civilization" that dissapeared without leaving any trace could be inspired by the legends of the Maya, a mexican tribe who sunndely dissapeared years before the conquerors arrived, so many made up stories of they being from the space and what not, mainly because they were advanced for the age..