I think we will get a 1800 or maybe even a 3200 skin for amumu. He is so an iconic champ in Runterra (got an own song, THE sad-face of LoL and so on) He has 2x 1350rp skins but in my opinion they are just 975 skins. The potentional for giving him an awesome skin is huge. Imagine the idea of an ultimate skin that desciribes the sadness of Amumu in game with spells and emotes ( changing emotes and VFx for : losing an ally , meet a lore important person , loosing turrets. Example: when amumu lost in a close area an ally he willhug sometimes the air as a symbol of the lost friend.
So before I go to deep in the idea of a skin. I think next amumu skin will be a big one or they are goind to give him a VGU soon that he will get no skisn until then and afterthat all of amumus skins will be cool then.