Since the new patch gave some breakpoints to classes that can‘t be reached. There probably are some new units on their way. Since the buffed classes are: Gunslinger, Brawler, Shapeshifter and Blademaster, im guessing the new units will be champs from Ionia, with a new Origin class tying them together.
Gunslinger - Jhin
Brawler - Lee Sin
Shapeshifter - Kayn
Blademaster - Irelia, Master Yi and Kayn
Kayn and Yi may even be units with three classes.
For Kayn - Shapesifter, Blademaster and the new Origin class
For Yi - Blademaster, Assasin and the new origin Class
What do you think?
EDIT: Im a bit unsure about blademaster on Kayn, since a sythe is not really a blade. Another theory I have that his transformation will affect his Class. Like if he transforms into blue Kayn, he will get Assasin and if he transforms into red Kayn he will get Demon. Probably based on the enemys teamcomp.
As for abilities on the other Units, Jhin will probably either have his passive, with more damage on his 4th shot, or his Q, the bouncing grenade.
Lee Sin may have his kick, kicking a unit back, damaging and maybe knocking back other units too.
Irelia will maybe have her E or Ult.
And Yi probably his Q, since its his most iconic ability.