I also use forward slashes but wouldn't have a problem adjusting to a ruleset you define. The customer isn't always right in this case.
2.0 could be a perfect compromise if you care enough about build times, don't you think?
Edit: come to think of it, i kind of even answered my own question. The prefix could just as well work as identifier. Something like:
release/2.0 -> tries:
release/2.0.yml -> "file doesn't exist or invalid"
release.yml -> "file doesn't exist"
circle.yml -> "file doesn't exist"
Finally, the introduction of a
config.yml (configures circleci) and
integration_test.yml) (defines/executes a "PR run" [to avoid the ambiguous word "job"]) would seem a logical next step if this is happening.