So what you have is a fork, with a fully implemented feature, that didn't make it back upstream.
This happens all the time, and is the nature of open source. No project is obligated to take your contribution, and that happens for a myriad of reasons that you are not obligated to understand.
It's fundamentally a human problem, not a software one. There's nothing wrong with the software here—it does everything required and more to be able to manage the codebase.
Take your fork, explain the situation in the README and let it be. It'll be in the fork graph and the list on Github. People can find it. If they like your feature, maybe they'll use yours instead. If enough people get behind it and ask for it, or say "hey this was in a PR, why wasn't it merged?", the pressure could be enough for the original author to just accept the PR.
In any case, this is not a problem with the pull request feature. It's a simple collaboration problem, and a PR is only one method of communication you can use to solve it. If you give up after throwing a PR into the void (not that I'm saying you did), you shouldn't expect instant success.
This happens all the time, and is the nature of open source. No project is obligated to take your contribution, and that happens for a myriad of reasons that you are not obligated to understand.
It's fundamentally a human problem, not a software one. There's nothing wrong with the software here—it does everything required and more to be able to manage the codebase.
Take your fork, explain the situation in the README and let it be. It'll be in the fork graph and the list on Github. People can find it. If they like your feature, maybe they'll use yours instead. If enough people get behind it and ask for it, or say "hey this was in a PR, why wasn't it merged?", the pressure could be enough for the original author to just accept the PR.
In any case, this is not a problem with the pull request feature. It's a simple collaboration problem, and a PR is only one method of communication you can use to solve it. If you give up after throwing a PR into the void (not that I'm saying you did), you shouldn't expect instant success.