The Switch, with its ability to play on a screen or a handheld, is exactly what I've been wanting for 20+ years.
Nintendo has nailed it. In future iterations I'd like to see improved specs and ergonomic changes as you and other posters have mentioned. That's about it.
A direction they could go is VR. I have a Quest 2 and I really enjoy it. It's possible Nintendo could enter that space. But they don't have any need to and I don't want to see them to.