There are strong rumours again of the Switch Pro coming, in 2020 as well. I'm rather dubious of this as I'm not sure if it's that worth it for Nintendo from both a commercial and requirement aspect.
I mean, if they can get it out in the Spring/Summer, then they may get some good sales, but I think if it's being released to try and take away from PS5 or Xbox sales, it probably wouldn't. People will be saving their money for these products this year, so Nintendo would be best focusing on software until next year IMO. My expectation is March 2021 which seems like a better time, with the Switch being four years old and most people who wanted a next gen console early would have got it in the previous holiday period just gone. Historically, early releases on new consoles are cross gen games which can run on the weaker machines, so Nintendo probably wouldn't have huge issues getting versions of some of these games on the current hardware. However, going forward they would need to release a more powerful machine just to be able to keep tabs at a similar level they are now (eg. Games like Doom, Witcher 3, Wolfenstein and so on).
I'm probably way off with this and we see a Switch Pro come out in June or something near the Pokémon DLC and it plays old games at better quality. I just think around March 2021 makes a bit more sense and hopefully Nintendo can get another couple of years out of that before needing to release the next, even more powerful version. Whatever the outcome, I don't think this next console upgrade from Nintendo will run games at native 4K anyway. They'll probably focus on trying to get games running completely stable at 1080p.