Since Riot has expanded skins, and now they all happen in separate universes or alternate time lines/dimensions, would it be safe to assume that the Pool Party skins and the Aprils Fools skins take place in the original League universe, where the League and summoners still exist?
The Pool Party universe is its own thing.
Where everyone likes to party.
Also there is a pool.
The universe closest to what you're looking for is the Warden/Marauder universe, which is in homage to the two original factions, the Magelords and the Protectorate.
Unlikely The champions of the old League universe were still representing their factions. I don't think people like Darius and Garen would put aside their differences and splash around in a pool together.
All of these separate universes remind me of what Marvel did during their Secret Wars saga involving every universe.
I look forwards to the many various versions of 
meeting each other, each with a individual quirk
Also the reveal that 
is part of a time-space singularity created by his abuse of the timewinder. Each version of him finally able to reunite and form his true self with the help of 
or maybe not :-)
I'm not sure why that would be the case.
As far as I'm aware the skins weren't necessarily canon back then and even if they were I don't see why these ones should be part of the old canon(where the league was for the most part serious business,some champs still wanted to kill each other outside of the league)
