I figured it out. The actual place to look into is/was epi-cms/widget/ReadOnlyContentList  - this component has a protected method, called _getBaseSettings() which returns configuration item, with direct reference to formatters.contentItemFactory() method.

So what I did, in module initializer I have put together following code:

define([
    "dojo",
    'dojo/_base/declare',
    // Parent class
    'epi/_Module',
    // Commands
    'alloy/AlloyFormatters',
    "epi-cms/widget/ReadOnlyContentList",
    // epi
    "epi/shell/dgrid/Formatter",

    "epi-cms/core/ContentReference",
    "epi-cms/dgrid/formatters"
], function (
    // Dojo
    dojo,
    declare,
    // Parent class
    _Module,
    AlloyFormatters,
    ReadOnlyContentList,
    Formatter,
    ContentReference,
    formatters
) {

    return declare([_Module], {

        initialize: function () {
            this.inherited(arguments);

            /*
             * Overriding default implementation of _getBaseSettings() method
             */
            ReadOnlyContentList.prototype._getBaseSettings = function (contextMenu) {
                
                /*
                 * This part is copy/pasted from original implementation
                 */
                var titleSelector = function (item) {
                    var reference = new ContentReference(item.contentLink);

                    return formatters.title(item.name, reference.id, item.contentTypeName);
                };

                var thumbnailSelector = function (item) {
                    return item.thumbnailUrl;
                };
                
                /*
                 * Here I build reference to my implementation of contentItemFactory() implementation
                 */
                var alloyFormatter = AlloyFormatters.contentItemFactory("name",
                    titleSelector,
                    null,
                    contextMenu,
                    thumbnailSelector,
                    undefined,
                    undefined,
                    true);

                /*
                 * Returning object  - only `formatters` option is overriden, rest is as in default implementation
                 */
                return {
                    store: this.store,
                    queryOptions: this.queryOptions,
                    formatters: [alloyFormatter],
                    deselectOnRefresh: true,
                    sort: this.queryOptions && this.queryOptions.sort
                };
            }
        }
    });
});

now my code runs :)