There is a possibility that Luffy will fight Akainu next arc because Oda hinted at Sabo being in danger
And even when Sabo's situation was unknown, Luffy already expressed the worry of his concern
So depending on Oda's direction, if Luffy finds out that Sabo is in a death sentence by the marines or something of the sort, i could see him wanting to go to mariejoa to save him
Which could then potentially make Luffy fight Akainu next arc, especially with Oda constantly claiming we're close to end of serie(so could make sense). Could make sense power-level wise as well considering post-Wano Luffy will be the one to just enter the top tier bridge, where he won't win against Kaido properly(with help of SNs weakening Kaido), but with Akainu being the first top tier Luffy would win against on his own
If it doesn't happen next arc however, i believe it'd be too late for Luffy's progression, and thus making it more sense if Akainu was actually Sabo's fight
And even when Sabo's situation was unknown, Luffy already expressed the worry of his concern
So depending on Oda's direction, if Luffy finds out that Sabo is in a death sentence by the marines or something of the sort, i could see him wanting to go to mariejoa to save him
Which could then potentially make Luffy fight Akainu next arc, especially with Oda constantly claiming we're close to end of serie(so could make sense). Could make sense power-level wise as well considering post-Wano Luffy will be the one to just enter the top tier bridge, where he won't win against Kaido properly(with help of SNs weakening Kaido), but with Akainu being the first top tier Luffy would win against on his own
If it doesn't happen next arc however, i believe it'd be too late for Luffy's progression, and thus making it more sense if Akainu was actually Sabo's fight