the steam deck already emulates lots of switch games (and some ps3 games) well and perfectly handles anything under that. the z1e/7840u is a stronger cpu than what the steam deck has, and will be even stronger in emulation
the only thing to watch out with the ally is that the device has a hardware design flaw with the sd card reader and controller that hasn't and likely can't be fixed until they come out with a sequel
i throw my deck down to 3-7 apu tdp when playing visual novels or emulating low powered stuff and get like 6 hours of battery life. if i had an oled it would be even better.