So, did Pulsefire Ezreal just confirm every skin line that Riot recognizes?
To compliment the fact that Ez is time travelling, dimension hopping convict, he has a literal truck ton of lines towards other skin lines, viewing them as different parts of a timeline, or part of a different universe.
If you haven't seen his interactions video yet, here it is.
https://www.youtube.com/watch?v=tlgD3GhABBU
So, just to list off all the skin lines he has interaction's towards (and mind you, there are A LOT of them)
- Academy
- Arcade
- Arclight
- Arctic Ops
- Battleboss
- Battlecast
- Bilgewater Burning Tides
- Bilgewater Dark Water
- Blood Moon
- Cosmic
- Culinary Master
- Dark Star
- Debonair
- Dragonslayer
- Dreadnova
- Elderwood
- Eternum
- Fables
- God-King
- Headhunter
- Hextech
- High Noon
- High Stakes (Card Theme)
- Justicar
- Lancer
- Luchador
- Mafia
- Marauder
- Mecha
- Odyssey
- Omega Squad
- Omen of the Dark
- Order of the Lotus
- Order vs Chaos
- Pentakill
- Piltover Customs
- Pool Party
- Prehistoric Hunters
- Program
- PROJECT
- Rift Quest
- Riot
- Road Warrior
- Snow Day
- Snowdown
- Soccer
- Star Guardian
- Steel Valkyrie
- Story Book
- Sugar Rush
- Super Galaxy
- Toybox
- Vandal
- Victorious
- Warden
- Warring Kingdoms
- Winter Wonder
- World Breaker
And lastly, but most obviously, Pulsefire.
Only 3 I can think of that are not referenced in his lines are Dragon Trainer (which can kind of be coupled with Dragonslayer), Halloween skins, and other music themed skins (like Pop Star Ahri), which is kind of interesting considering all 3 of those are being represented in upcoming skins.
Obviously, I'm sure there isn't any real defined list of skin lines, and it's very possible they're creating new ones as we speak. That said, I'd say with confidence that PFE is a pretty good indicator of just how many skin lines we have.
EDIT: Just realized he doens't reference Valentine's Day skins either, like Heartseeker, or Sweetheart. So, there's that.