what XPath REALLY should have evolved into was a more format-flexible path language with format-specific extensions as needed.

You can probably already do that just fine: ignore attribute nodes, and e.g.

    {"menu": {
      "id": "file",
      "value": "File",
      "popup": {
        "menuitem": [
          {"value": "New", "onclick": "CreateNewDoc()"},
          {"value": "Open", "onclick": "OpenDoc()"},
          {"value": "Close", "onclick": "CloseDoc()"}
        ]
      }
    }}

    /menu/popup/menuitem/*[last()]/preceding-sibling::*[1]/value

selects "Open". Something along those lines.

Maybe relax nodetypes so they can be pluggable per-language, but I'm not sure that's even useful or necessary.