Tons of misinformation bouncing around in this thread, so I'm gonna try to clear up some things based on what I know/suspect.
- This is a converter, not a mod. This will not lead to Xbone "hacks." This will not aid piracy. This will not aid homebrew. Thread title is misleading and should be changed to something like "Xbox One USB converter unlocks support for KB&M, DS4 and more."
- This converter works as a passthrough. I can't be 100% sure, but it should essentially work like a pad hack for an arcade stick; a legit Xbone controller is used for authentication, while the converter takes the input signals from whatever you have, converts the value into what the Xbone expects, then sends it to the console. The "scan for inputs, then convert, then send" step may introduce some lag, although lagless converters are already available for PS3 and 360. However, the authentication should mean that the console will not be able to tell the difference between a CronusMAX and an Xbone controller, so it will likely not be patched out. That is an assumption, however.
- The advantage of using a mouse instead of an analog stick to aim comes from the fact that games use translation data from the absolute position of a mouse over time to calculate how far, and in what direction, to aim. Your mouse is at point Y; 1 ms later, it is at point Z; it moved X amount in W direction, so that is how much your aim should be adjusted right now. On an analog stick, you move the stick, and your aim is altered by a fixed amount every time the game updates depending on how far the stick is from center. Your aim speed increases from slow to fast at the same time. On a mouse, your aim speed is as fast as you can move your mouse. The key is this: changing the input method does not change the interpretation method. The game will not suddenly aim as fast as you can move your mouse just because you used a converter instead of a gamepad. Even if you throw your mouse across the mousepad as fast as you can, your aim will never move faster than it would if you simply held the analog stick at the edge of its rotation. Thus, there is no advantage for mouse and keyboard players using a converter over gamepad players.
And for some conjecture...
There is little practical reason for MS to not, at least unofficially, continue to allow 360-licensed controllers to work on Xbone. The fact that they're licensed for 360 means that they meet a certain input method standard; they'll have all the same buttons the Xbone controllers have. At the very least, they'll know what the hell all the buttons do automatically. The PS4 allows developers to support PS3 controllers, even though they might not necessarily be supported in the OS for navigating menus just yet. So for people who want to use arcade sticks, for example, no extra hardware is necessary on PS4 (assuming developers support the old stuff).