I truly believe these devices are some of the most enjoyable to use. You don't just use them because you HAVE to, you use them because they are simply a joy to use. I believe that adding mouse/trackpad support to the iPad is a matter of when, not if. You can already connect a wired keyboard to the iPad. This should really be an accessibility feature. Having more input options never hurt. Think of the Apple Pencil. The iPad can be used without it, but when paired, it allows you to use the iPad in more ways.
What I do not understand is that Apple prides itself on wireless connectivity; that is, wire-free, simple setup. With the introduction of USB-C, what would be the point of connecting to an external monitor if only to view what is already on your iPad screen. For presentations, an Apple TV and AirPlay work great. I can only hope that upon connecting to a monitor, that the iOS interface "expands" for a 4K display and permits the use of a bluetooth mouse to navigate the 4K display; at the very least, I hope the iPad screen enters touchpad and keyboard mode to allow for cursor control and keyboard input while connected via USB-C to a monitor.
An OS strengthens when well thought out features are implemented; not everyone will use those features, ex. accessibility features (high contrast, less motion, etc.), but for those who do use them, the experience is just further enhanced.