Alternate Dimension Outfits
I was trying to think of a type of champion skin that could be shared among every champion. Since not every character can work with the debonair, pool party, dragon slayer, etc. Sort of how they all have their classic skin, each champion would have this alternate dimension skin. Where you know that it is that character, but something about their core concept is different. The outfit though wouldn't change the character enough to the point of them being unrecognizable. Such as how HoN did with their skins.
This is sort of a way for champions to go outside their specific lore and be a different version of the character already there. Their personality may be different or they could just have a different appearance. But it basically gives the character the ability to have a different style to them.
Like a human Orianna, a holy Karthus, a feminine Vi, a Malzahar that uses robotics instead of magic, or a completely robotic Zed. Just to give a few examples of what could be done. And it wouldn't change the character entirely, but enough to make them seem like they aren't the same champion in the lore.