I thought the Mecha Kha'zix skin was really sweet, and a few ideas came to me. Let me know what you think.
Mecha Kog'maw: Kog'maw really seemed like a perfect idea for the skin. Give him the metal body with spikes, robotic red eyes, and a plasma cannon for his tongue.
Mecha Akali: Ok, maybe not full-mecha, but a futuristic, cybernetic implants look with a cyber armor and a set of energy kama like the designs for Kha'zix.
Mecha Skarver: Another perfect selection for the skin collection. a full body of dark grey metal with a blue energy spike for his stinger. As for his exoskeleton ability, he could create a series of energy barriers around him in replacement to the crystal armor.
Mecha Volibear: One of my friends told me that when he got Volibear, he said that there weren't any good skins for him, and I thought it wouldn't be such a bad idea to make one for him too. Give him the badass, war-machine or steampunk kind of look.
Mecha Warwick: Nothing special, I just thought it would be sweet seeing him with a skin like Mecha Kha'zix with energy claws. With a quick idea, I was thinking that when his blood scent is activated, his eyes would light up when an enemy has low health.
Mecha Zyra: Another idea with cybernetic implants, except with mechanical plants (no pun intended :P) she can be able to use cables instead of vines, and her plants summoned would be completely mechanized.