Forks don't have to be hostile. A perfectly reasonable way to react to an overwhelmed maintainer is just to do a friendly fork. Keep the original name, attribution, git history etc, update the README and start acting as a trustworthy lieutenant. You can review stuck PRs and merge them into your own branch, whilst also merging with upstream master. After a while if you seem to be making good calls the original maintainer can do a bulk merge from your branch to bring in many PRs at once, and maybe add you to the repository.