It's important to remember that consumer-facing apps is just a part of the market; and even with consumer-facing apps, the user interface is often only a small part of it.

Even totally plain-looking device could be full of innovative research: a network router which uses completely new kernel. A new network protocol or a compression algorithm. New programming language. Automatic verification and/or fuzzing tools. A network of internet of things devices which share no code with any of the existing OSs.