so too partially answer my own question, I found an article... (https://gregwiechec.com/2015/12/propertylist-with-images/)

"Unfortunately, grid formatters doesn’t allow to return deferred results from formatters, so code that returns promise won’t work"

my code is returning a promise. :-(

Answering my own question, had to change my approach, as you cant use Dojo in this instance to load content, you load the content in c# and add it as metadata which Dojo can then read. Article I posted above explains most of what you need. Here is a quick summary of what I see as the important bits:

Making extra data available to Dojo:

public class PropertyListUrlExtenderAttribute : Attribute, IMetadataAware
{
    var extendedMetadata = (ExtendedMetadata)metadata;
    /* extendedMetadata.Model and extendedMetadata.Parent.Model *may* contain model data */

     var urlCollection = new List<PropertyListItem>();
    /* 
        snip, fill urlCollection 
        where class PropertyListItem { string Id { get; set; } string Url { get; set; } }
    */
    if (!extendedMetadata.EditorConfiguration.ContainsKey("mappedUrls"))
    {
        extendedMetadata.EditorConfiguration.Add("mappedUrls", urlCollection);
    }
}

in the above code, extendedMetadata DID NOT contain model data, and instead we save data in a cookie (the ID of the current model), which was used when filling urlCollection with data from the current model (load cookie, read content ID, load content from db). remember the whole initial problem was that we could not load content about the current model from Dojo without using asynchronous code. The data was stored via the block's controller (in a cookie), and ONLY when in editmode.  if (PageEditing.PageIsInEditMode) { /* store currentBlock's ContentLink.ID in a cookie*/ }

Reading the extra data using Dojo (and using _getGridDefinition to display extra data):

define([
    "dojo/_base/array",
    "dojo/_base/declare",
    "dojo/_base/lang",
    "epi-cms/contentediting/editors/CollectionEditor",
    "app/editors/extendedFormatters"
],
    function (
        array,
        declare,
        lang,
        CollectionEditor,
        extendedFormaters
    ) {
        console.log("ExtendedCollectionEditor");

        return declare([CollectionEditor], {
            _getGridDefinition: function () {
                var result = this.inherited(arguments);
                console.log('Loaded...');                

                if (this.mappedUrls != null && this.mappedUrls != undefined) {
                    for (var i = 0; i < this.mappedUrls.length; i++) {
                        if (this.mappedUrls[i].id != null && this.mappedUrls[i].url != null) {
                            extendedFormaters.setMapping(this.mappedUrls[i].id, this.mappedUrls[i].url);
                        }
                    }

                    result.link.formatter = extendedFormaters.urlFormatter;
                }

                return result;
            },

            onExecuteDialog: function () {
                var item = this._itemEditor.get("value");
                
				if (this._editingItemIndex !== undefined) {
					this.model.saveItem(item, this._editingItemIndex);
				} else {
					this.model.addItem(item);
				}                
            }
        });
    });
	
------------------extendedFormaters.js---------------------------------

define([
    // dojo
    "dojo/_base/lang",
    "dojo/Deferred"
],
    function (
        // dojo
        lang,
        Deferred       
    ) {        

        var elementUrls = {};

        var extendedFormatters = {

            urlFormatter: function (value) {

                if (!value) {
                    return '-';
                }
                if (!elementUrls[value]) {
                    return value;
                }

                return elementUrls[value];
            },

            setMapping: function (contentLink, url) {
                elementUrls[contentLink] = url;
            }
        }

        return extendedFormatters;
    });

in the javascript above, _getGridDefinition is where the magic happens, it's a function that is called to format the contents of the propertyList (so we replace that function), and in result.Link above, Link refers to a property on our EpiServer block, so you would have named your property you're trying to style differently probably. 

Hi Noel,

I think this is virtually the same problem I had and the same solution I came to here: https://jakejon.es/blog/showing-the-friendly-url-of-a-content-reference-or-url-property-in-a-propertylist

It's worth mentioning that Episerver don't officially support using a Url in a PropertyList so a block is normally the preferred approach.

/Jake