In a forum post, Riot Ququronn announced that champion portraits in game will now show a portrait from the skin you’re using!
Ultimate skins, like Elementalist Lux and DJ Sona, always did this, but now they’re adding it to every other skin and taking it down from the list of ultimate skin features.
The splash art icon won’t change on anything but that little circle above. It’ll look really cool to you, but the mini map, kill screen and scoreboard will all still show the base skin. After all, some splash arts are a big harder to make out and new players could easily get skins confused with entirely different champions. It’s also much easier to quickly glance at the mini map and recognize Lux immediately, while recognizing Elementalist Lux’s fire form might be a bit trickier. Clarity is the key!
The new feature will be included in the patch 7.16 Public Beta Environment cycle and added to the game when that patch goes live.