- We don't know if Sakurai's even involved with the port (assuming that the port is happening).
- Tying back into my eSports mention, Nintendo likely wants to replace the Wii U in the competitive community as soon as possible. Hard to do that if they release the Switch version too close to EVO, forcing them to stay on the Wii U. Of course, if that "Nintendo's pushing for eSports" rumor isn't true, disregard this bulletpoint entirely.
- As mentioned earlier, Smash 4 is still Nintendo's biggest Amiibo-seller. And while yes, there are other Amiibo-compatible games in the Switch's library (MK8, Splatoon, BotW), Smash 4 is still the biggest one of the lot that supports Amiibos (namely due to its large cast).
I agree with you, Neoxon. If Nintendo can get Smash ready day one, that will unequivocally be to their significant advantage. It can only benefit them to have Smash and its amiibo available. Also from the eSports perspective as you mentioned as a possibility. Also, it's just a big seller. Though, OTOH, if we forget amiibo, on Wii U alone MK8 and Splatoon are the bigger titles, so if Nintendo has other amiibo plans or wants to make a separate splash for Smash and amiibo or doesn't want three Wii U ports/all three of those major titles at launch, perhaps then Smash wouldn't be as likely to be at launch as one or both of MK and Splatoon. (And then Splatoon also is getting bigger in eSports I believe, though certainly not to the Smash level.)
Though, Smash's combined sales on 3DS and Wii U do push it past Splatoon (though it's still been the combined 22M sales of MK7/8). Edit: it was helpfully pointed out to me below that I have the #s wrong here, Smash actually did better than Splatoon on Wii U alone. So, there are various arguments then to be made for Splatoon being launched ahead of Smash or the other way around -- is it better to launch the biggest of the three (MK) and least big but still hugely popular (Splatoon) together to give Smash plenty of breathing room for its own launch? Or bigger to lead with the heaviest hitter or two? Or launch each of the three individually, with only one of them at launch? Maybe Nintendo would feel it's likelier to get people to buy more amiibos alongside Smash specifically not on launch day when they're also buying new HW vs. alongside a separate Smash release when they're maybe only buying the game otherwise?
Additionally, I wonder if we will see Mario Kart amiibo at launch, especially if Smash does not make launch. They surely want to get people to buy a lot of amiibos when they go to the store to buy Switch. Smash are the most popular amiibo though so no question those would be the ideal bet, and I wonder if there is realistically shelf space for both. Maybe just a limited line of MK amiibo, then. I wonder how often we will see amiibos packed-in with retail titles, also. I imagine quite a bit on the larger titles.