I think there's one important thing that hasn't been established. This is a configuration option for binderhub deployments to deviate from each other in terms of what images they produce from the same repo, with the ability for deployments to either override or default exclusions (TBD in implementation).

It seems in order for this to be useful, you'd have to have a situation where many repositories regularly have files that should be excluded from images that follow a particular pattern and no repos have files that follow the same pattern that should be included, but it is not reasonable or feasible to suggest repo owners specify exclusions. Does such a situation exist in practice? If not, I think we should wait for an actual deployment to make its case that its images are too big, simple exclusion files would fix the problem, and their users cannot be expected to resolve the situation in their repos.