One For All should force a unique skin/chroma for each player
Like how in any other game where the same character gets picked the color or shading at least changes to differentiate them. All skins/chromas should be unlocked for the champion that gets picked. I don't play with names on so seeing the same skin for every player makes the game mode significantly harder.
And for champions with < 5 skins, idk maybe Riot could make sure to release at least a chroma pack of the base skin for every champion.