Huh, I'd been assuming the Switch 2 would be AMD Z2 based. I guess they've managed to convince nVidia to make them another SoC. A little surprised, would have thought nVidia would want to use any spare fab time for AI chips, though maybe they have some older process capacity?
Why wouldn't they just use an emulation layer? There have already been several Switch emulators that run on x86 in the wild.
Because it is a mobile console, therefore battery life is a limitation and adding an extra layer of indirection (and therefore, work) will drain that battery faster.
I hate to break it to you, but battery life will be at the bottom of the list of Nintendo's concerns when giving you backwards compatibility. If Yuzu was able to get 2.5-3 hours of battery life on the Steam Deck (which isn't that far off from what it gets playing a lot of "native" games) essentially flying blind, Nintendo should be able to do at least that.