I was under impression Android is a Java VM (Dalvik) running on top of Linux kernel, meaning it could theoretically work with any base OS capable of running JVM

I was under impression Android is a Java VM (Dalvik) running on top of Linux kernel, meaning it could theoretically work with any base OS capable of running JVM. While it may use some linux-only features, is it really hardwired to it so much it cannot be ported elsewhere?