Just took a Riot survey about Morde and Prestige skins, from what i took away from it.
He may get a new skin after several years without but it would most likely be of a Superior quality only. Frankly i would be extremely disappointed if that is the Case.
After years of neglect i kinda hope for more.
I could be wrong, but i have become a pessimist due to Years of mistreatment of my Favorite character.