I previously felt also that Nintendo had denied NX would be a hybrid, but this thread convinced me Iwata never actually debunked a hybrid, so you may find it worthwhile also:
http://m.neogaf.com/showthread.php?t=1253682
Regardless, as you said, things can definitely change over the development cycle. It will be very interesting to see how close the rumors are to reality. Given the IMO significant reputability of WSJ, Eurogamer, Emily Rogers, and LPVG, I expect them to be pretty much right on the money. If any one of those leakers are considered less reputable to you, perhaps any of others listed you might feel more comfortable believing. By no means do I think that these leakers all share the same source or that they didn't get corroboration from independent sources for their leaks. So to me personally, these rumors are as official as they can be without being technically official, but I understand each of us may reach different conclusions about their veracity, since all we can do is decide for ourselves since we don't have any firm official word to go on. (Though, I should say I also believe the comment from The Pokémon Company is a hint in this same direction, though I understand interpretations vary amongst many in this thread on that front also.) As I said, it'll be very interesting to see just how close these rumors are to reality!