6" recessed can light to track light
Caveat: I've not done this, nor do I know NEC. I'm basing this off my experiences

I think the pendant conversion kit might suffice. Your track lighting (the second one, not the first) will be screwed into the ceiling directly. The pendant adapter uses the hot and the neutral of the light socket and then probably grounds off the fixture itself (hence the metal clip). Your track lighting would simply pigtail to the wiring adapter.

The catch here is that the cover for the power adapter is probably not large enough to cover the hole for the can light. And the track might not sit flush over the metal adapter in the picture (if it's flat it might, but if it's not flush with the ceiling, or a convex cover, it probably won't). So it might not look very neat. I'm not sure if they would make a cover large enough, but you might be able to fabricate one from a flat plate if needed (i.e. cut the plate to size, cut a hole in the middle and then screw to the fixture)