While I agree that Nintendo doesn't compete with any of the current-gen consoles, it is debatable that they don't offer as good a package as the others since this is - in the end - a matter of personal taste/opinion (I do agree with you, though, that Nintendo's - or rather - the Wii U's offerings are lackluster in comparison).
It's out of question that Nintendo will ever go third party, but still...after much thought and as it is right now, I can't think of any reason why Nintendo shouldn't go third party and release their top-notch games on other platforms.
In the broadest sense I'd also love to see only one gaming platform which is supported by every developer (be it Sony, Microsoft, Nintendo, Ubisoft, Activiosn, etc. etc.). This, however, would destroy almost any competition and that - in the long run - will only be bad news for us gamers.