eclev91 on "Expanding the media library select options"

I'm trying to add an option to the media library select dropdown that will allow the user to view only images uploaded by a particular author - I don't want this to definitively be the case, I want the option via the select box.

Right now I've overridden AttachmentFilters.All's createFilters function to add my own filter like so:

add_action( 'admin_print_footer_scripts', 'add_author_to_filter_object', 51);

function add_author_to_filter_object() { ?>
	    <script type="text/javascript">
	    // Add custom post type filters
	    l10n = wp.media.view.l10n = typeof _wpMediaViewsL10n === 'undefined' ? {} : _wpMediaViewsL10n;
	    wp.media.view.AttachmentFilters.All.prototype.createFilters = function() {
				var filters = {};

				//new one
				filters.featuredAuthor = {
					text: 'Images Uploaded By Featured Author',
					props: {
							status:  null,
							type:    null,
							uploadedTo: null,
							orderby: 'date',
							order:   'DESC',
							featuredAuthor: true
					},
					priority: 5
				};

				_.each( wp.media.view.settings.mimeTypes || {}, function( text, key ) {
					filters[ key ] = {
						text: text,
						props: {
							status:  null,
							type:    key,
							uploadedTo: null,
							orderby: 'date',
							order:   'DESC'
						}
					};
				});

				filters.all = {
					text:  l10n.allMediaItems,
					props: {
						status:  null,
						type:    null,
						uploadedTo: null,
						orderby: 'date',
						order:   'DESC'
					},
					priority: 10
				};

				if ( wp.media.view.settings.post.id ) {
					filters.uploaded = {
						text:  l10n.uploadedToThisPost,
						props: {
							status:  null,
							type:    null,
							uploadedTo: wp.media.view.settings.post.id,
							orderby: 'menuOrder',
							order:   'ASC'
						},
						priority: 20
					};
				}

				filters.unattached = {
					text:  l10n.unattached,
					props: {
						status:     null,
						uploadedTo: 0,
						type:       null,
						orderby:    'menuOrder',
						order:      'ASC'
					},
					priority: 50
				};

				if ( wp.media.view.settings.mediaTrash &&
					this.controller.isModeActive( 'grid' ) ) {

					filters.trash = {
						text:  l10n.trash,
						props: {
							uploadedTo: null,
							status:     'trash',
							type:       null,
							orderby:    'date',
							order:      'DESC'
						},
						priority: 50
					};
				}

				this.filters = filters;
			};
	    </script>
	<?php }

Which adds the option to the select box as expected - great. Now I want to catch the ajax query and adjust its parameters accordingly:

add_filter('ajax_query_attachments_args', 'featured_author_media_filter');

public static function featured_author_media_filter($query) {
	    if($query['featuredAuthor']) {
		    $featured_author = get_field('featured_author', 2); //get from front page
		    $query['author'] = $featured_author->post_author;
		}
	    return $query;
	}

This is where things go poorly. It seems like my if statement there is never true. If I do a dump or something before it, the ajax loading of the media library fails, so I know at least my filter is being called. Is there something I'm missing? I don't feel like this whole thing is very well documented and I admittedly know next-to-nothing about Backbone.