There will never be an Ultimate Skin Battlecast. Reason being is Cho'gath is Battlecast PRIME Cho'gath. Anivia and Skarner will be normal Battlecasts like Urgot and Xerath.
But honestly Udyr is technically the Prime candidate for Ultimate skin, Ezreal was honestly a fan favorite goal and a test. They had to really force his to make it work and of course they decided Megaman style, which isn't really bad or anything just most champions will be harder to do.
Eternum Nocturne would have been a nice one to be an Ultimate. But ultimate skins are a LOT harder to make than a legendary skin or a champion.
The ultimate skins you have to take something that is already created a add an evolving feature to it without making them clash with each other.
Ezreal is an explorer, and researcher so Pulsefire design fit his lore, not only that but his abilities are all things Megaman could do or at least similarly.
Spirit Guard Udyr just takes his link to the spirits to a whole new visual level and shows that as he gets stronger in each connection the link gets more visually seen. --- Xbox 360 GamerTag: HolyKnight22 PSN: CrimsonDivide