I don't see it being cross gen tbh. The only two times Nintendo has done this in the past had, IMO, three big circumstances that contributed to the decision to release 2 SKUs:
1) The failure of the previous system tied with the hype for the game. Both BOTW and TP were games with huge amounts of hype releasing late in the life span of a dead console where releasing it to that small of a user base made 0 sense.
2) Change in format/input. The gamecube to wii transition saw a change from standard to motion controls whereas the Wii U to the Switch saw a change from disc to cartridge which I believe helped inform the decision to make two SKUs. If the Switch 2 is backwards compatible and only really has better specs, I don't see Nintendo wanting to invest in a second SKU for what is effectively a performance mode (something to my knowledge Nintendo has never really promoted a game on)
3) They were both Zelda games. Zelda is in a unique space where it is held in incredibly high esteem by hardcore gamers while also having some mainstream potential with more casual audiences (yes, even before BOTW). I really believe a big part of BOTW's success was in appealing to hardcore Nintendo fans, new audiences and most importantly, lapsed gamers in an equal measure that I don't feel any of their other franchises really do (including Metroid).
Considering their recent statement about a June direct and the successor seemingly being a ways out, I am leaning towards Switch 1 only but I would not rule out it being moved to Switch 2. I just don't really think it will be cross gen.