Well, Issue 3 of the Lux comic is out, and with it came a pretty interesting wham scene near the end. While fighting Sylas, a knock from Garen's sword gives him magic that he then uses to punch the daylights out of him.
It's absolutely wonderful and it's just what I personally wanted from their fight, but the interesting thing is: this scene only hints at, but does not reveal, the nature of whatever power Garen uses. All we have confirmed is that it's connected to Kayle's celestial magic. But is it in Garen's sword? Garen himself? Both? Something else?
As you can see on LordRedStone's general Issue 3 thread, (linked here: https://boards.na.leagueoflegends.com/en/c/story-art/xcrR2bEH-spoilers-lux-issue-nr-3-feedback-discussion-and-questions) theorizing on that is the main topic of discussion. Some people want Garen to be magic, some people don't want it, some would rather have it be part of the petricite discoveries, and no one knows anything yet for sure.
So I thought it would be interesting to poll people's theories and desires for what'll be revealed about Garen down the line. Feel free to discuss below as well.