I mean, I'm okay if the game never gets upgraded, I'm having a blast with it as is. It just makes sense business wise for Nintendo for multiple factors, including that they will probably need invest in a crossgen transition because they won't be able to support the new hardware with only brand new games, and they will have one of their biggest games of all time right there having its legs cut short by the Switch phasing out. It's kind of a no brainer.
And the argument that they never did it before is simply not true, they did this several times, especially on the Switch with lots of enhanced Wii U ports. It's just the format would be a bit different this time because the environment and context is different.