Possibly the following file contains more options, though admittedly I have not spent much time looking for them. This is the file that contains the information used by `SyntaxInformation`

    ToFileName[{$InstallationDirectory, "SystemFiles", "Kernel", 
      "TextResources", $Language}, "FunctionInformation.m"]

This file contains a lot of options, both "Symbol options" and "string options". Not all "kinds of options" are listed here, at least the "option" `"OptionNames"` of `SyntaxInformation` is not present here. The file also does not appear to contain nested options.