A thought-provoking post, but let’s get our terms straight here. If SMS is or some other “simple messaging” is the primary interaction modality, then that is the UI–which is very different from something having “no UI”.
In my Medium response to this post, I mentioned that “even your smoke detector” has a UI, even if that UI is “just” a little light, a button, and some annoying-ass low-battery chirps at 3 o’clock in the goddamn morning.
The really interesting questions getting raised here are around what a user interface is, and how much of it can you take away. Can you shield people from the complexity of buttons and search boxes and hamburger menus? Can your app do its thing through a “chat” modality? Or is that going to be confusing? Can you lose the visual interface all together, a la Siri?
These are great questions to be asking, and I’ll admit that these are things that I’ve taken for granted.