Oh, Nintendo.
As it stands now, Nintendo is the only company with first party games that are worth a damn[footnote]Unless you just aren't interested in Nintendo titles, like me, then there isn't really a console worth getting right now.[/footnote], and even though they don't have the third party support of Sony or Microsoft, most of the third party games that are out right now are also out for the last gen consoles, so unless you are super into having the best graphics, there is little to no point in buying the Xbox One or PS4 right now, making the Wii U the only console out there right now that is worth getting. That being said though, when Sony and Microsoft actually start to release some games that are worth a damn (probably starting with Halo 5: Guardians for the XbOne and Uncharted 4 for the PS4), then that might change, but as it stands, the PS4 and the XbOne are selling solely on the promise of better graphics than the last gen consoles, and the promise of some new games (at some point).
Would I personally like it if Nintendo went third party? Of course I would! I would love to play some of their best titles like Bayonetta 2, Mario Kart 8 and Smash without having to buy a console.
Does Nintendo need to go third party? Hell no. Nintendo benefits from a fanbase that is probably more zealous than Microsoft and Sony combined, and they do this by having a few core franchises that the develop and innovate over and over again. Nintendo had a spectacular year in 2014, and that only goes to show that Nintendo is in no way failing.
Is the Wii U less successful than the PS4 or Xbox One? Yes.
Does it need to be more successful than the PS4 or Xbox One? No.