Okay! Now that I've had time to formulate a better response! First off- YES, second; perks to all these Boyo's

Sora--
-Probably would be the most level headed to the Xehanort situation and help unite the cast
-Reverse mentoring; Axel may be team babysitter but Sora has just as much to teach him about being a good person
-Has the benefit of also triggering "real" emotions out of Axel most of which will be awkward, because he hasn't had time to adjust to swapping sides and doesn't have a cool way to save/reintroduce himself this time
-actual Islander can teach these idiots how to actually live at sea
-Oh the memory confusion "Hey about Castle Oblivion..." "I never saw you at Castle Oblivion?" "..right."

Squall-- badass, cool! We all love a good Squall
-likely wouldn't struggle as an introvert with all the chaotic gremlins around. Just needs something to give him a goal?
-could likely be implemented into the FF gangs around already

Leon-- all of the above really, plus
-Technically share a hometown?/Radiant Garden, could make headcanons about it
-Same age range, have been through the same things; it's possible to relate to KH nonsense
-Someone who knows about Org XIII and isn't an immediate friend could lead to amusing side eyeing at eachother
-potential of helping co-parent key-kids