What I really want to see is more clothing sliders. More specifically, I'd love to have separate "loosness" sliders for not only the shirt and pants, but also the jacket, undershirt, and underpants. For example, I could have a tight-fitting shirt on, but my jacket is loose. Maybe even looseness sliders for the gloves and shoes/boots? I'd also like to be able to separately tune the looseness for my sleeves. Maybe we could even have a cuff width slider like the pants do?
Some more ideas:
Ponytail width - One end of the spectrum would be a very thin ponytail, the other end would be as wide as the rest of your hair can be.
Ear Shape - maybe square-type ears, round ears, pointy ears, etc.
Ear Length - Going along with ear shape, ear length would be a fun addition. I could imagine some kinda elf av with 6-inch long ears.
Transparency slider for hair - I dunno about you, but sometimes when I see old folks, even if they have a full head of hair, I can usually see their scalps. This one is just kinda for fun, really.

More Spike Sliders - There are bunches of stuff that could be added to spiked hair. Spike width, spacing, which side of the head (left, right, front, back), angle/direction, curve, and stiffness (whereas the spikes we have currently would be 100% "Stiff", perhaps as one decreases the stiffness, the spikes would start to droop over?).
Collar Shape - When lowering your collar line, perhaps one could choose whether one wants a v-neck shape, or a semi-circle shape, or a squared shape. I'd also like to be able to lower the collars over the shoulders in addition to down the chest and back. Maybe even have separate, left and right sliders so one could have the appearance of wearing a "lopsided" shirt.
Shirt/Undershirt Length - The shirt and undershirt currently cut off EXACTLY at the pants line. It would be cool if they could go lower, like the jacket.
Pants height - Going the other direction, the pants seem to stop exactly at the shirt line. Maybe there could be the option of "hiking" them up a bit?
Layer Switch - Right now, the clothing layers are predetermined. Socks go under the shoes; shoes go under the pants; pants, go under the jacket, etc. I'd like to be able to choose the order of my layers, so I can have my shoes go OVER my pants, or wear my underpants outside my pants. I know there are currently texture-related ways around this, but it would be more convenient to be able to simply choose which layer goes where.
Well, I think that's all the ideas I have for now... A few of em I came up with just while writing this post, heh.