Speaking to CNET in an interview, Apple’s VP of interface design Alan Dye was quoted as saying, “As critical as the hardware is at playing the role distinguishing Apple Watch as Apple Watch, we think the watch faces play a pretty big role there as well, which is why we’ve been so careful over the years, despite the fact that there’s wide variety, to have a lot of consistent design elements.”
Dye also points towards the complications as a way for users to personalize their watches, while at the same time maintaining Apple’s own aesthetics. “If you look closely, the watch hands are always drawn exactly the same way, despite the fact that they show up in different colors. We think we struck a really good balance. The watch faces themselves, they provide a canvas for third parties for sure, and a template that they can [use to] create multiple complications and turn a watch face into their watch face, and that becomes the interface in some ways for their application.”
So, if you were hoping that we would see Apple open up the Apple Watch for third-party watch faces, you definitely shouldn’t be holding your breath.