Since Judgments are now in some weird, semi-canon limbo, there needs to be something to replace the character development that happened in hers. Lux's Judgment brought a painful reminder of her past, catharsis, and... a home within the League. It was a path to recovery, a road that could very possibly lead to happiness and fulfillment.
I don't know how they'll replicate that development, but I think it's best if she takes those steps, for the most part, alone. Aside from the summoners creating the test (who don't really count, they're just the memory machine, or whatever), Garen played only a very small role in the Judgment. It would feel--for lack of a better term--wrong if another character became integral to that "same" character development.
When Riot eventually gets around to rewriting her lore, I hope they don't flanderize her in-game traits. I worry that they might strip away so much of her character, and leave only a shallow ghost of her old personality behind.
As for which direction would like to see Lux story go, I'm not sure; somewhere happy, I suppose. (I'd love if it Riot dropped the arbitrary Ezreal pairing, but there are probably too many people that find it adorable. I wonder how many of them actually care, and how many of them just ship the smart blonds together and move on after six minutes.)