Riot your on the right track with mordekaiser
First of all let me just say this splash art is incredible! But I'm here to talk about one champion in it particularly, that being the king himself, Mordekaiser.
We all know Mordekaiser is an old worn out champion and is due to get a complete relaunch much like Sion sometime in the future. While we don't know when this is I know Riot has already begun talking about ideas for it, and I think how they portrayed him here shows exactly how his kit and overall character should feel. They NAILED it in this picture.
Mordekaiser should NOT feel like a bulky undead juggernaut like Sion. He should feel tall, and menacing as if he is looming over the battlefield watching his "pawns" scurry about. He is a king and should feel like it. His figure is much like a stout tower, not too bulky but still fortified and intimidating. Having his overall character mold into this opens up new ideas for his kit as well. Instead of leaning towards the more tanky "soak up damage" spell caster they were trying to change him into on patch 5.4 it allows him to stick with his identity as a caster/Mage.