We've got #5276 filed, but the main reason for removing env is that users simply don't understand how the merge logic works. (And I don't blame them, I barely understand it, and might not be able to describe it to you.

That said, there are other places where we merge, so we should still figure out a better story around how configurations get merged together. Primary cases where we merge now:

• Config files can extends: "./other-config" and things get merged
• Programmatic options to babel.transform are merged with .babelrc options
• "env" blocks are merged with their parent configs
• If we do [Feature Request] feature similar to ESLint "overrides" (config based on glob) #5451, we need a clear story around merging for specific files.