Hmm, are you sure this is needed? Does it not work in conda if you don't have this installed?

I attempted conda remove python.app, and the following packages had to be removed with it:
imagecodecs-lite-2019.12.3-py38h64e0658_0
libllvm8-8.0.1-h770b8ee_0
pyct-core-0.4.6-py_0
spyder-4.1.3-py38h32f6830_0
tifffile-2020.5.11-py_0

So I think the package might not be OS-specific, but software-specific. Sorry, I just judged from the package description that it might be a package many people install by default.

Maybe instead of putting this package with the ones already listed, we can put it in a new list of potential packages to remove, but not everyone might have, just so people can have more information?

The package does look like it is a OSX specific package. This means if you include it in your environment.yml repo2docker won't be able to build the image.

Thinking about the fact that the list of packages not available on linux is very long (and can change) made me wonder if we should add a sentence here that tells people to "check if a linux version of each of your packages exists by visiting https://anaconda.org/conda-forge/packaegnamehere and looking for the linux icon" or some such. However we need a way to deal with the different channels so maybe we should link to a search page on anaconda.org instead?

Yeah that makes sense to me, we could link to the conda default channel pages, and also mention that non default packages might also exist in other channels (and treat that as an advanced use case)