User blog comment:YourPrivateNightmare/Brace yourself/ A time to appreciate/@comment-24165677-20140902155456

I believe Viktor will get the Ultimate skin, he goes along well with the entire thing about evolutions throughout the game (like when Ezreal gets a point in his ult, or Udyr maxes an abilty/stance). He's getting a kit update too, which will allow him to eventually be able to buy all three Hex Core upgrades, which will make for some awesome features with an ultimate skin.

This might be a weird point, but I think Xerath is too "popular" for the ultimate skin. Udyr was rather unpopular when he got his, but he suddenly got played a ton. I could see Riot do this to someone like Viktor.

My second guess would be Xerath, as he only has three skins, and because I overall think it will go to a midlaner, and definitely not a jungler/toplaner (Udyr) or an ADC (Ezreal). Oh, and of course because of this whole Ascension thing.