Note that CC-BY-ND-3.0 only applies to some of the icons used in the app. I’d honestly open an upstream issue on that.
Another possibility is to build all of the code in one derivation and then have a second derivation that adds the icons. The former would be Free, so hydra could build it. The latter is unfree but since it only adds a few icons, it could be built on the user’s macine in under a second.
Yes please. My machine is not too bad really, but Yuzu is heavy and needs a while to build. This solution sounds like best of both worlds. I will try to take on this task, but my Nix knowledge is limited enough that it will take me a while and if somebody wants to have a go I wouldn’t mind. Will even be a good example for me.
That sounds like a good task to get into Nix. Though I’d urge you to ask about this issue upstream first.
Using unfree assets is an issue and I don’t even want to know how the GPL plays into that. The icons aren’t really an essential component and could easily be substituted with any other that looks vaguely similar.