After using NixOS for a year, I've found it to be a great operating system. When the software I need is on nixpkgs, things work out great. When I need to install software from outside of nixpkgs, though, it can become a pain. Trying to figure out the quirks of some closed source application can become pretty complicated. It would be great to package it and contribute it back to nixpkgs, but a lot of the time I just want to have the application working as soon as possible.
Since Ubuntu is a more standard linux distribution, I hope that it's better supported by some of these closed source applications. By dual booting, it's possible to get the best of both worlds.