I look at a watch, any watch, and I think it should be circular. The argument that a square interface makes more practical sense for a digital display is valid, but on the wrist and in everyday use it makes no sense at all.
Apple has some parts of the software already in place for this. The fitness rings and the weather app are examples and many third party apps go circular as well.
Losing a bit of text in messages and notification would be a disadvantage, but I am 100% certain that a round Apple Watch would be a huge improvement and a chance for Apple to show that they can design more than just fancy looking technology. This is a chance to bring some real emotion to their products.