I think if Zelda is as polished as Nintendo wants it to be by summer 2017, it's coming out in summer 2017. Mario Kart 8 and Splatoon have proven that a release during that time of the year doesn't necessarily preclude a game from selling well or moving hardware units (relatively speaking), and Zelda had a lot of hype surrounding it during E3 2016 from a lot of the people that Nintendo is trying to win back with Switch. If all goes well and Nintendo has a strong first six months with the console, it shouldn't matter which big series they slot into the Holiday 2017 spot; ideally, they'll already have a lot of momentum going into that part of the year.
Mario Kart and Splatoon being ready by summer isn't a given either. We're all assuming that they're enhanced ports or heavily leveraging their Wii U counterparts so they should be ready for release by then, but that might not end up being the case (even if it does seem like the likely scenario). On the flip side, I guess there is that rumour from Laura Kate Dale that the Smash 4 port is planned to be ready within the first six months, so that might be an alternative.
All of this is, of course, assuming Zelda doesn't come out in March 2017 (which this rumour doesn't totally rule out).