[Skins] Ultimate Skins?

So, the last ultimate skin, Spirit Guard Udyr, was released almost a year ago, and there was a lot of speculation beforehand, lots of Riot teasers, etc. Is Riot still developing them, or has the continual ratcheting of skin quality made ultimate skins too hard to make stand out?

Any champions you think would be particularly well-suited to an ultimate skin, or concepts that deserve to see the light of day?