using side by side with nixpkgs

[KiaraGrouwstra]

Is your feature request related to a problem? Please describe.

I would like to conscientiously use unfree packages, so would rather not default to nixpkgs-unfree for all my packages, but I feel it might make for a more elegant way of plugging holes into my otherwise-free setup than doing so the usual way.
I managed to separate nixpkgs and nixpkgs-unfree for regular packages (e.g. Zoom), but have yet to figure out how to achieve something similar for e.g. Steam, which I had installed using option programs.steam. There, setting programs.steam.package = ... turned out not enough to
ditch Steam-related stuff from nixpkgs.config.allowUnfreePredicate.
It would be cool if anyone had further tips on how to explicitly use nixpkgs-unfree for separate stuff including programs.

Describe the solution you'd like

Separately use nixpkgs and nixpkgs-unfree, such that one could explicitly mark unfree stuff as such.

Describe alternatives you've considered

Wholesale switch to nixpkgs-unfree and no longer remain as aware which of my packages are unfree.

[zimbatm]

You can use both as flake inputs and use them side by side already. What can be tricky is how to get the multiple inputs into your NixOS or home-manager configuration.