Since Lux is a light mage, she should be able to reveal stealth champions. Every time she throws her Q, W, and E, it should reveal stealthed champs along the projectile travel path. And if she marks someone, they should be revealed also. i don't think it will make her too strong, she'll still probably get punched in the throat and die before she can snare a talon or rengar. But it would be a nice added utility close to her character concept.
Counterpicks do not exist in league - Riot
*except for Lee Sin - Riot
By that I mean there are a whole lot of abilities that should reveal stealth. I don't even think Lux is a good candidate for that line-up. Stealth doesn't mean you hide in the dark - it has no connection to that, when hit by some kind of light, they will get revealed. In fact, most stealths in fiction, when explained scientifically, revolves bending light AROUND the characters to escape refraction of light from enemies - so they should take reduced damage from Lux instead, as Lux focuses all on light-based spells while stealth characters technically have ability to bend light around them.
Meanwhile, nothing in a fantasy setting is supposed to make sense. Stealth champions dont get reduced damage from Lux while in stealth.
And Lux is not so overpowered right now so Riot will not touch her, even if it's utility-based changes.
I love this idea
