This has been a dream of a lot of COH players and Titans to boot.
However, there are a lot of underlying programmatic factors that would make this most difficult.
A bit of levity on the topic, sure the concept of an out-of-game costume creator sounds awesome, but when it boils down to it... why would it be necessary?
It's not like Mids, that saves you millions if not billions of in-game inf to see what your numbers will be properly speced. That is however not in the game.
Costume Creator however IS. And as far as I've seen, you can modify your character until Kingdom come... it won't charge you until you are finished.
I'm not a big fan of re-inventing the wheel and this definitely is one of those situations.
If you're looking for a tool that helps you create 3D figures in a easy to use interface, there is an application called "Poser", I believe it is in its 9th version and has progressed leaps and bounds in how awesome it is. Of course not free.... but just throwing it out there.
I know SuckerPunch has been wanting to do something like this for awhile, but it is very hard to get our hands on GOOD opensource libraries that support OpenGL or alike. Which are required to support the ability to view a character renders in any amount of dimensions.
Plus the PIGGS are nothing more than giant relational zip files that has all the 2D texture and image files for our in-game characters so it would require the PIGGs to be on the same computer it's being run on, which is a bit pointless... since you can just run the game and get the same functionality.
All in all, of course, a great idea... just not logical.