watchOS 4.3.1 code includes NanoTimeKit framework, which is a key component for the watch faces.
Apple Watch is likely to support third-party watch faces in the future, per 9to5Mac report citing a code found in watchOS 4.3.1. For now, Apple is the one responsible for providing watch faces, and some of the existing ones bring to life popular Disney and Pixar characters. But Apple has been controlling watch faces for quite some time now, and for no clear reasons stated by the company whatsoever. However, some widespread speculations more or less point towards Apple’s desire to have a full authority over both branding as well as experience.
watchOS 4.3.1 code includes NanoTimeKit framework, which is a key component for watch faces. It seems to suggest implementation of a developer tools server, which is believed to make interaction with Xcode running on a Mac possible, thus increasing chances of letting third-party app developers create their own watch faces in the future. However, it is not clear at this time if Apple is positive about bringing this change to their watch ecosystem. But if they are, we can probably expect this new capability to come into practice with watchOS 5.
Also Read: Apple Watch 3 Review
Last month, there was a report that Apple Watch Series 4 could sport 15% bigger display than that of Watch Series 3, courtesy KGI Securities analyst Ming-Chi Kuo. It is also said to feature new sensors in addition to heart rate sensor, improved health monitoring and longer battery life. Kuo has also predicted that close to 22-24 million Apple Watch units are expected to be sold in 2018, resulting in about 30% year-over-year (YoY) growth.