Just adding on to this, I do think the "up-specced OG hardware" approach something Nintendo has done before. Upgrades like GC to Wii and Game Boy to Game Boy Color are really just boosts to the clock speeds and RAM, they don't have anything specifically included for BC reasons (unless you're counting GameCube memory card slots). They really are just iterations on the same hardware. Similar to the New 3DS, on modded consoles you can run GameCube games at Wii clock speeds and they almost all work without issue.

On that subject, the fact that Nintendo says the compatibility won't be 100% is potentially encouraging. If the Switch 2 was just going to downclock compatible parts to their Switch 1 performance and was otherwise identical, you'd expect all games to work. The reduction in compatibility could be because games are going to be running with Switch 2 clocks across the board, which most games should handle just fine and a small handful may not.