I think it'd be really cute if at some point Lux ended up in the following situation
Picture this: Lux is investigating some ruins for a possible threat to Demacia (i.e. Noxian spies) when the ruins start shaking from an earthquake. She loses her balance and falls off a high ledge, but before she hits the ground she is caught by... you guessed it, Ezreal. Complete with a "princess carry" catch.
Cute way to start their relationship? I just thought it'd be cute after seeing this image while watching a playthrough of Fire Emblem Echoes. https://vignette.wikia.nocookie.net/fireemblem/images/0/0f/Conrad_and_Celica.png