Free Skin Day or Unlocked skin day

I don't know what it was called or what it was for but once a long time ago riot had a special event where all the skins for every champ was unlocked for a day or if anyone remembers what it was for I have been playing league since Ezreal used to heal with his "W" so yea long time.I was wondering if anyone has heard anything coming up like that in the future or something? Maybe even do everything unlocked all champs and skins for some special event in the future that would be cool. Disable all the champs in ranked but in all other modes you can play with new champs and see the fresh skins.