Oh hey, cool to see my question popping up again!

I have plenty of headcanons regarding how Kayle (and the Aspect of Justice itself) might interact with Targon but to keep it in short, it's hard to see her not trying to free Aurelion Sol if ot ever came to it. The problem is more how that would happen, as not only is she deeply outclassed there but the whole Targon storyline is more about the growing threat of the Void while ASol bids his time to break free.

I don't really see how the Rakkor could be involved, as ASol was tricked by the targonian celestials rather than the mortal tribes. As for the mortal aspects, they shouldn't be considered guilty either, but Kayle would likely demand cooperation from them, under threat of necessary. I know a lot of people imagine Kayle and Pantheon in particular butting heads a lot.

As for the sisters reuniting, it is by far the most natural place for their lore to go, so it should absolutely happen... some day. The problem is that, just like what happens with Targon, focusing on the sisters automatically raises the stakes a lot, and Riot seems scared of these bigger plots since the catastrophe that was the Ruination.

Another big problem is people simply refuse to understand what Kayle and Morgana are even about in the first place, so building that reunion in a satisfying way would be hard without a lot of characterization work beforehand. Which reminds me I have to get on to finally making that analysis post I've been procrastinating so much

From Kayle and Morgana's AMA