I noticed a few times that that nbdev-based project like fastai2 requires contributors to update nbdev, often times only discovered after a PR failed the CI check. I wonder if this condition can be caught locally in developer’s sandbox.
e.g. Perhaps a feature like: the repo contains the latest, required version of nbdev used by the CI on github, and that when run locally on a repo, the nbdev_* tools can detect/advise/abort if it finds itself obsolete? When the repo later needs to use a newer nbdev, bump that version number/file.
I know “always update nbdev to the latest git” is one solution… but we humans don’t always remember, and this check may save a few hours of debugging broken build/CI 
If it sounds like a useful feature to add, I’ll be happy to help. Thanks.