What prevents Cargo from adding `[bench/bin/example-dependencies]`?

epage:

Third-party tooling that processes dependencies, particularly ones related to supply chain management

Does not look like a big issue to me. Without bench deps support such tools would simply ignore the section, which does not seem like a bad fallback to me.

epage:

Does cfg(bench) work?

No, it was one of suggestions to "solve" this problem in the linked issue.

epage:

dev-dependencies affects

Yes, I know. And my statement above was in the context of that. I probably should've added "deprecated in favor of [test/bench/examples-dependencies]".