There's no telling what Nintendo will do. They've made some inconsistent decisions in the past about how they treat older consoles during an upgrade launch. But I doubt Nintendo will close its doors to the millions of existing Switch owners. It's
still selling well, even though it's been more than five years. They'll likely want to continue selling software to them. So I expect a "better on Switch+" experience for something like Breath of the Wild's sequel, while still making it available on both consoles. They're going to say things like 4K on Switch+, and "1080p" on Switch Standard.
But as the months and years go on? Yeah, they'll distance themselves from the original Switch's hardware limitations, because time marches on. Good riddance, that thing is slow as fuck these days.
Ocarina of Time Remake released only on the 3DS back in the day, so even though I had a DS, I couldn't play it
The 3DS and DS had very different hardware. It wasn't just that one was 3D and one wasn't. Just like how the Wii U had very different hardware than the Wii despite the similar naming convention.
Nintendo hasn't been great at its console names, or messaging hardware differences. They're married to the Apple-esque idea that hardware should be simple and uncomplicated, so they don't like to talk up the specifics of upgraded hardware, which leads to confusion around the launch period.
The most tumultuous example of this was in 2011. Did you know that
when the Wii U was first announced, Reggie didn't get on stage and say "Our new console is named the Wii U." No, no. That's just toooooo hardware-focused. Instead, the first mention of Wii U was Reggie talking up a bunch of bullshit about how "U could mean Utopia," and finally said, "This is the new controller for Wii U" showing a picture of the Wii U controller. "It's infinitely complex and yet perfectly simple. All at the same time." Okay..... So... What the fuck is Wii U? Is it a controller for the Wii? Is it uh.... a new handheld? Nobody knew what to think. Then, after the show, they'd later say that oh yeah it's a new console, and here's what it looks like.
I also recall that around the recent release of the Switch OLED, people had to do teardowns to determine the hardware spec differences (not many other than the oled—better battery was the one that stuck out to me). Whereas Nintendo's messaging was: SCREEN BETTER.