I don't really think that the Ace/inerithed will/Mera Mera arguments work if we are talking about a possible confrontation with Akainu. I don't see what they even have to do with Akainu.
In contrast, I certainly see the reasoning behind the Zoro/Oden inherited will (strike Kaido down and to open the Wano borders)/Enma arguments and what motivations tie them to Wano and Kaido.
I also don't think we have seen Sabo reference Akainu's name once (and the opposite as well).
I could see is Sabo encountering Akainu and/or briefly protecting Luffy from him before his fight with Akainu continues.
But him joining the Akainu fight still doesn't make sense to me, given all the elements I wrote about before.
We'll see.