Right now for the Switch hardware that we currently have, all Nintendo has to focus on is getting Japanese and mid range publishers / developers.
They have always had dicey relationship with EA and other major Western third parties besides UBI Soft, plus logically if the third party wanted to port the majority of their titles to the Switch it is doable short of them building their game exclusively with 4K or some other high end tech in mind. As successful as the Switch is globally there are plenty of ways to support it whether it is with a port or a separate team that works on lower spec games that could be released on it. However with new hardware a year or two away, most won't bother to invest that heavily in learning or adapting to aging tech.
Japan development for better or worse is much more compact and used to tighter budgets, plus globally while not in the same realm as CoD or FIFA they have a strong audience who as we have seen with the Switch and PS4 this generation can be a force to move products.