Niri looks really cool. I've used tiling WM before but scrolling is a unique take, perhaps more productive for some folks?
Nushell is a good one. I do data science for a living and it'd be nice to have the shell handle some small data transformations instead of writing a script in python. But all the syntax and behavior is very different than bash, so I've been afraid to start because of the learning curve.
My drive to nix was so I could simply manage what packages I had installed with a text file. If I removed something from the file, I expect it to be uninstalled. I never found a tool/wrapper for apt to do this.
If you want to start with nixos, I would take whatever distro you are on and install nix and then home manager. Then, you can slowly migrate your user configuration over without starting from scratch. That worked really well for me going from ubuntu to nixos.