I don't think Nintendo is dim enough to release a Switch 2 next year and try to re-release Breath of the Wild for it.
In fact I'll go out on a limb and suggest that based on previous console lifecycles, and the way the 1st party support tends to trail off towards the end of the cycle so they can dev on the new console so it can have a release line up, and the way that (current) Switch releases are powering through like there isn't a new console coming out in a year, that we're looking at a very high probability of a 100% backwards compatible console here. Otherwise I think they'd be holding more of this stuff back for the next release.
With the way consoles work nowadays it'd be pretty easy for them to release a new engine for BotW/TotK for a Switch 2 that just comes down as a patch like any other when you plug the cartridge in. And you hardly even need a new engine just to push out a higher res display, as emulators prove.
Nintendo is also in a different position this time around, as the WiiU, DS, 3DS, etc had such different hardware that remaking a game for the Switch was essentially a necessity, whereas I expect the Switch 2 to be a Switch with faster hardware.
...and still be able to play Breath of the Wild on it. (Although, to be fail, the mainstream user probably won't be doing that.)