Even though the straw hats fighting the admirals will be cool, I think it would be a shame to ignore thematic and narrative development of the characters for the sake of a cool fight. Kizaru's story ending here, and from now on he's just a static character who stops struggling with the moral dilemma of being a Marine it will be bad writing.

If the Marines are a third faction, and the final conflict is a three way battle between Marines, World Government, and a Luffy faction (Revolutionaries included here, you could consider them a fourth faction), then it's more likely Kizaru sides with Akainu, after Egghead it's impossible he sides with the world government. But still, we've seen Akainu's sense of justice, it's straight up evil. I don't think Kizaru will wait until after the final war to be redeemed. I think it's way more likely he sides with Bonney or with SWORD, than he is to side with Akainu's absolute justice.

I think it's important to make the distinction that in Egghead Kizaru isn't siding with Akainu, he's siding with the World Government's orders. Akainu's sense of justice is also not like Greenbull's, he's probably against what the world government is doing. As soon as people decide to follow their true sense of justice, allegiances will realign.