My idea is that at the beginning of a match kayn chooses the "rivalry" for that game. And throughout the game he works to become one or the other, just like Rhaast or Shadow Assassin.
What this means is that he would choose skin lines that compete, or as I call it a rivalry.
Ideas of Rivalries are:
Project VS Program
Star Guardian VS Dark Star
Dawnbringer VS Nightbringer
Mecha VS Battlecast
Pulsfire VS Hextech?
Archlight VS Soulstealer
The Left side is Shadow Assassin, the right side is Rhaast. It would be the same as it currently is, more melee battles you get Rhaast early and more ranged battles you get Assassin early ( In this case, left side early or right side early. An example, more ranged battles you get Dark Star early ) .
I understand this would take ALOT of work. You making 3+ skins in one. Also, I dont know what base Kayn would be... any ideas?
Another concept I have would be themes that oppose each other. Like Ninja VS Samurai? Cowboy VS Bandit? Superhero VS Supervillian?
( If anyone is getting a ultimate skin I highly doubt it would be Kayn but mabye some of these concepts could be used for a legendary or epic skin? )