It depends when it happens. If '19 or '20, then definitely an upgrade and not a new system. After that, it then depends on how much of an improvement it is.
Personally, I think the Switch update that's been teased will be a smaller, lighter, cheaper model, considering that the biggest titles planned this year (Animal Crossing, Pokemon, Link's Awakening) have their roots in portable consoles. So a "pro" model might not be for a few more years, in which case they might just choose to make it a whole new console.