So, I recently did something like this on Xenforo. I'm just curious as to what exactly you would like to see in a theme. For example, do you want multiple colors without having to install multiple themes, do you want adjustable width by just having to click a link, do you want links sorted into a dropdown, etc. Just post an idea you've had that you'd love to see implemented in a theme and if there's enough support for the idea, you can be sure you'll see a theme with it there (As long as it's possible, of course).
I've seen many new designers are adding a jQuery script to add the ability of changing colors. They mostly are using Color Picker:
http://www.eyecon.ro/colorpicker/ . You may play with it know how to install it on the forum.
The multiple colours feature will be much easier in MyBB 1.8
I personally like to see themes that use common sense. There are themes that just pile tons of features in without a second though - resulting in a massively slow loading time and clutter.
Sleeker login/registration forms.
I have already integrated colorpicker in my Encolor theme.
I am now trying to make on hover profile cards just like IPB with css and only HTML.
May be I don't know what's going to be next !!!
These are all very nice input, I look forward to working on certain designs relating to some of the mentioned features.
In response to Uncontrol, I've definitely got something in the works to that regard (Well, login at least).
Also, euantor, I agree with you there, people creating a theme then putting features around it (Throwing stuff in just because it's everywhere else) just seems like the wrong way to go about it imo. Makes them seem out of place, and like you said, too many slows the page load. I want to take certain features and build the theme around them, instead, if that makes any sense. xD
But yes, thanks for all the input so far, anything else?
In reference to what Eric said, highly to many features is going "over-board", a professional should always be able to include details and features to his/her design, but one has to keep in mind, that too many details, and features is reason to name a designer "un-confident" or "un-professional", taking risks such as adding subtle details and subtle features will set apart a good design from a bad design, all though the "good" designer will know which details and features to keep and which to remove.