This can be done with a pretty simple custom property editor. If you are unfamiliar with how to create them, check this out: https://our.umbraco.com/documentation/Tutorials/Creating-a-Property-Editor/

Here's a simple example doing what you are looking for. You'll need to update aliases etc. but this should get you close.

For this I added a NestedContentDD folder to App_Plugins. That folder contains 3 files:

• package.manifest
• NestedContentDD.html
• NestedContent.controller.js

Here are the contents of each file.

package.manifest

{
"propertyEditors": [
    {
        alias: "NestedContentDD",
        name: "Nested Content Dropdown",
        editor: {
            view: "~/App_Plugins/NestedContentDD/NestedContentDD.html"
        }
    }
],
"javascript": [
    "~/App_Plugins/NestedContentDD/NestedContentDD.controller.js"
]

}

NestedContentDD.html

<div ng-controller="Custom.Namespace.NestedContentDDController">
<div ng-if="message !== ''" ng-bind-html="message"></div>
<select name="ncVals" ng-if="ncOptions.length !== 0"
                    ng-model="model.value"
                    ng-options="opt.item for opt in ncOptions track by opt.item">
</select>

NestedContentDD.controller.js

function NestedContentDDController($scope, contentResource, contentEditingHelper) {
$scope.ncOptions = [];
$scope.message = "";

// If you don't know the id of the node with the Nested Content you are pulling 
// your values from you're going to have to get it from somewhere first.
contentResource.getById(1170)
    .then(function(data){
        // This is only looking at the default variant. If you have more you'll need to handle that.
        var props = contentEditingHelper.getAllProps(data.variants[0]),
            ncItems = props.find(function(prop){ return prop.alias === 'nCStringVals'; });// Whatever the property alias is of the nested content property.

        if(ncItems){
            if(ncItems.value.length > 0){
                $scope.ncOptions = ncItems.value;
            }else{
                $scope.message = "<em>No options have been entered.</em>";
            }
        }else{
            $scope.message = "<em>Unable to find options property.</em>";
        }
    },
    function(data){
        // Error handler
        $scope.message = "<em>Unable to find referenced node.</em>";
    });} angular.module('umbraco').controller("Custom.Namespace.NestedContentDDController", NestedContentDDController);

The editor doesn't love having a controller pasted in, so the end of the file is ugly, but it looks like it took it all.

Once those files have been added you'll need to create a new data type that uses the new property editor. The property editor will be named "Nested Content Dropdown" in the list (see package.manifest). Then just add a property to your content type using the new data type where you want your dropdown (tongue twister!).

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