What if, way into the future, there were a season of "The Lion Guard" that serves as a prequel/parallel/midquel to "The Lion King II: Simba's Pride"? In this season, Kion and his friends have grown into adults. They still have many adventures protecting the Pride Lands, but at the same time, they take part in certain events of Kiara and Kovu's adulthood in the sequel. It'd be just like in "The Lion King 1 1/2".
I'd let the adulthood stuff start when the lion cubs think okay we have some new friends and the Pride Lands are now safe so we should start choosing our mates. ( they feel like peace has returned)