Yes, it is unrealistic. Third parties don't trust Nintendo anymore. Pointing out some third party games managed to push over a million on the Wii doesn't mean much when you consider the install base of the system. It sold an absurd number of systems and only had an absurdly high attach rate for first party games. The Gamecube was just a casualty of the N64. There was some third party support, but it was notably lacking when compared to the PS2 that basically got everything.
Now look at the Wii U: third parties barely tried before the system was considered a flop and took the earliest out they could to not have to bother. They just don't care about Nintendo because they already reap massive profits across Playstation, Xbox, and PC. Similarly, it has hit the point where people who buy Nintendo consoles aren't doing it for third party support. The audience has been seriously trimmed down to those who buy Nintendo consoles for Nintendo games,, as plenty felt alienated by the Wii, and the casuals certainly didn't come back for the Wii U. Where Nintendo saw financial success with the Wii, they lost an audience, they lost yet another chance to actually earn third party respect and trust back, and now more than ever, third parties can port nothing to Nintendo and never care because it's easier to not bother for the minimal profits they would get.
Nintendo may secure some third party deals just because they have to get something going in between their games, especially in this day and age where development times can get so absurdly long with their team sizes and goals, but it won't be voluntary third party support unless there is a seriously strong showing of third party purchases on the NX by the consumers.