This sucks, but a problem we have in academia is that you can't reference a closed PR request at a top-tier conference like VLDB. If you wrote up your proposal as a referable document, you should rightly claim that you deserve scholarly recognition. Morally, you deserve recognition (which you are getting here, at least). It's decent of the author to admit he was inspired by you - there are others who would think it is easier to deny it. But there is no recourse, if it's only a PR.