I find myself reconfiguring my smartphone countless times; much more than my computer. Is there something that works like nix to define my config on a device, like apps, email, calendar accounts, etc.?
I don't think it'll be until I can have an appstore that rewrites my config with a new generation. Apps on my phone are much more spontaneous because its on me all the time and so much more general purpose. I can't imagine having to install uber and having to edit a config and waiting for it to evaluate derivation when I need to call a taxi right then and there.
Yeah on mobile it is definitely needed. On desktop I don't mind as much (but I'm often lazy so instead of properly adding to my system config I just keep nix running instead). On mobile there's no way I'm going to fumble around with nix expressions in a text editor.