I’ve read about people trying to contact Keith before. I understand it must be difficult for him – not having time or interest anymore, and probably not knowing what to answer. Who should he give commit and publish rights to? How does he know it’s not a malicious actor? I don’t know.
Maybe it’s better to start with a fork, and publish it on the JetBrains Marketplace. If enough time passes with great development, showing that the whole thing is genuine, then he might be interested in handing over the intellij-elm name (to help the community knowing which plugin to use).
At that point the new maintainer might even be trusted to get paid by Elm companies to work on it: Elm Camp session about editors and IDE plugins
So if you’re up for it, maybe go and fork, tweak and release?