Thanks for the response, Steve. Since the new stuff (the Smart System) is actually different hardware it cannot replace the existing stuff for all existing drive systems out there. In other words, the Kiox 300 only works with Smart System drives, which are different from all the existing Gen 4 (and prior) systems out there. I do agree with you that ultimately that is where they want to be. But I don't think they can sunset it anytime soon given the number of current drive systems out there and still being sold. So regardless of what Bosch does with the Kiox and Nyon, they will always be the most advanced system my bike can support (Performance Line CX).
I actually don't care much about navigation. I am more interested in the fitness tracking and data display. The Nyon can display more panels on a single screen than the Kiox so that was my deciding factor. Honestly, both the Kiox and Nyon are overkill for me, but I love gadgets, customizations, and data! Since Garmin cannot tap into the metrics from the bike drive system (user and motor watts, cadence, speed, etc.), and since the Nyon will allow me to play with the motor assist graphs, I think it probably fits me best.
I do like the smaller size of the Kiox better though. But here is what scares me most about the Kiox. The last straw for me with the Smartphonehub is that it ejected my nice phone out onto the pavement on a ride. The Kiox is only attached via magnets....so...I don't trust those magnets to not eject the Kiox too. I know the Kiox has a screw that can be used to permanently mount it, but then I cannot remove the head unit. So another plus for the Nyon for me is that the Nyon has a actual latch docking mechanism.