Yes in the end, I feel this will happen that Sabo will burn Akainu use MMnM power + insane HAKI.
And how exactly would Haki enhance flames?
For that matter, it was already established that Magu Magu no Mi is superior to Mera Mera no Mi. It's not Naruto, you can't simply break rules cause.
–- Update From New Post Merge ---
We don't know what their over all plan is yet, but eventually we cna expect the 4 Emperor's are gonna start taking each other out. Kaidou is preparing for something with his army of zoans, Blackbeard for the past 2 years has been on a DF hunt, and Big Mom well forget about her, i think her time is at an end pretty soon. Shanks really doesn't come into this because he's 1 of the "good" guys, and would prolly be more sympathetic to the Revolutionary cause given his ties with Roger/Luffy etc
That's not much of plan now, is it?
Also, I expect Akainu marines to be able to take down one Yonkou at the time. From what I've seen so far, revolutionaries don't seem nearly as strong as marines at the moment. Conflict with even one Yonkou would be disasterous for them. Which might happen, considering Burgess…