It's true that he's pretty old. His lore is also pretty... well, it needs an update.
So do a lot of champions, but first things first. ;)
So we're looking at him (from the narrative side) from more of that 'black knight' perspective, but also at who he was before he was encased in supernatural masochist power armor.
Interesting start. Here are some suggestions if they're not too late.
[NOTE: THIS is why Narrative needs to talk with us instead of just making decisions on their own. Maybe we can suggest something awesome you guys haven't thought of.]
As in, what drives him? What makes him the way he is?
People who make deals with the supernatural are often desperate. Kratos (God of War) was desperate for a victorious battle against Barbarians and pledged himself to Ares to get that wish. Most of us should be aware of the aftermath of that pledge.
Perhaps pre-armor Mordekaiser was a good but very arrogant knight (maybe Demacian) who fell from grace and offered a deal to any supernatural entity around. His offer was answered by the Shadow Isles and thus was born "Mordekaiser."
Why is his will to dominate and humiliate rather than to outright kill?
I forget who said it, but someone said "You can kill a man only once, but you can break him many times." It's tough being "numero uno" if there's no one else around to be your... number two. Also, if you dominate a person, you can make them do things for you out of fear/respect/whatever.
It could be that Morde may be trying to raise an army instead of killing his enemies.
We want to make sure we're preserving what people do like about him, while fleshing out what isn't there.
More suggestions:
• Keep the "heavy metal" theme. Reference new songs if Morde is going to have a kit change.
• New VO to get rid of the references to the summoner and the game ["As you wish, SUMMONER" and "You only need to click once, fool!] Also, keep the same voice actor! He's been really good to the community.
• Alternate laugh should be "Hue hue hue!"