Emulation is a lot nicer when it works, but it doesn't most of the time (most games have glitches, and a significant number don't work at all). It is OK for a third party emulator to not offer a perfect experience, not OK for Nintendo itself. It is impossible (not-viable) for Nintendo to create a perfect Switch emulator that works for all titles, that you can just plug a Switch cartridge on the new console and it will guarantee it will work without glitches, there is just too many corner cases.
To sum up, it is impossible for them to make a hardware compatible console, impossible to make a 100% compatible emulator, so the only option is to market it as a completely new console (not backwards compatible by default), then have a small curated list of backwards compatible titles (either thru their "virtual console", or something like Microsoft did going from the original XBox to the 360, where you could put the original game and it would download a patch for the new console, only compatible with a limited list of games). But this limited backwards-compatibility options would create a big break in the Switch lifetime, so not something to be undertaken while the console is still going strong.
To sum up, it is impossible for them to make a hardware compatible console, impossible to make a 100% compatible emulator, so the only option is to market it as a completely new console (not backwards compatible by default), then have a small curated list of backwards compatible titles (either thru their "virtual console", or something like Microsoft did going from the original XBox to the 360, where you could put the original game and it would download a patch for the new console, only compatible with a limited list of games). But this limited backwards-compatibility options would create a big break in the Switch lifetime, so not something to be undertaken while the console is still going strong.