I think you're maybe doing a little forest-for-treesing yourself here, Morello. True, until this point LoL hasn't had a mermaid-style champ - but it *does* have Rengar, Hecarim, Cassiopeia, Warwick, Nasus, Renekton, Udyr, Twitch and Wukong. Anthropomorphic champs aren't that unusual. More to the point, while Ironstylus may or may not have been talking about overall silouhette variation, this thread and others like it are talking about a specific kind of variation - the presence of markers of sexualization in a champion.
There's something I think of as the Halloween phenomenon - that is, a number of champions look like they purchased a sexy-[blank] costume rather than going fully with their concept. Zyra, for example, could have looked something more like this - http://bit.ly/107EFE2 - and Elise's human form suffers the same issue, although transforming into a giant spider makes up for a lot. Nami I think is on the lower end of this scale, but isn't without troubles. Despite the fact that in some ways she's a very monstrous champ, she still has a human skin coloured torso (reinforcing the woman-in-a-mermaid-suit look), an hourglass figure, and a heavy visual emphasis on her boobs. (its less a matter of size, though thats a factor, than of framing)
Diana proved that a female champ doesn't need to be sexual to be badass or attractive (I'll repeat what I said at the time - you guys really knocked it out of the park with her.) And as for male champs, I'd point out Singed and Swain as good examples of the kind of variety we're looking for in female champs. One is old and walks with a cane; the other is tall, skinny and lanky.
I guess it boils down to this. A lot of the time it feels like Riot's 'default setting' for female champion design is "variant on sexy woman." All we're really seeking is a default setting of "variant on woman" - which will sometimes be sexy, and sometimes more like Singed/Swain, but will most often be more like Diana, or Leona, or Katniss from The Hunger Games, or Korra from Avatar.
You will see some old types of archetypes that we've learned from - sufficiently "derpy" (without good humor or cuteness) or unappealing archetypes (old, crippled man who is supposed to be a tactician but is just a bird-wizard) aren't something we'll go towards, but finding what replaces them is the interesting part - and importantly how to make it both cool and differentiated.