I fully agree with you on built-in voice chat (the phone app is an horrendous solution), bluetooth headset support, and themes. Although I doubt headset support will work well when wireless controllers are used (bluetooth limits, which is why I believe Sony did not add bluetooth headset support to PS4).
I do not care too much about streaming services and music players and such, though it would be nice (might make me ditch my entertainment tablet; though I have pretty much done that with my smartphone) I guess and it would add superficial value to the system for those that are just looking at features (the one place I can see it being useful is for parents that have their kids watch streaming stuff on the Switch as opposed to on other more open devices).
A web browser falls in the same category as streaming services (a tad more useful), but seeing how pretty much the PSV, Wii U, 3DS, and PS4's browsers were used to hack the system (and even for Switch, the mini browser used to log into Wi-Fi hotspots was used by hackers to get information about the system) I doubt Nintendo would risk it.
Backwards compatibility would be great. Though a similar effect might be achieved with VC and Wii U remakes/ports (maybe they can add support for 3DS titles on the eShop later on).
