I was reading someone asking over at S2C about this, and I found myself curious as well. Do we know how to create more patterns for coats yet? I would assume they're based off alphas somehow, but do we know how it works? If not, I'm kinda bored, want me to poke around and take a look?

Well, you can do default replacements for them now, but I wouldn't really recommend it beyond for personal use due to the potential for conflicts if a bunch of folks start doing a replacement for one or two... Custom ones I don't think anyone's figured out yet, though there is research being done on it here, if you want to take a look and try to help figure it out: http://www.modthesims2.com/showthread.php?t=199958