Index: src/wp-content/themes/twentyseventeen/functions.php
===================================================================
--- src/wp-content/themes/twentyseventeen/functions.php	(revision 39262)
+++ src/wp-content/themes/twentyseventeen/functions.php	(working copy)
@@ -123,7 +123,9 @@
 
 		'posts' => array(
 			'home',
-			'about',
+			'about' => array(
+				'thumbnail' => 94,
+			),
 			'contact',
 			'blog',
 			'homepage-section',
Index: src/wp-includes/theme.php
===================================================================
--- src/wp-includes/theme.php	(revision 39262)
+++ src/wp-includes/theme.php	(working copy)
@@ -1824,6 +1824,16 @@
 		$config = array();
 	}
 
+	/**
+	 * Filters the allowed extra post args for starter content.
+	 *
+	 * @since 4.7.0
+	 *
+	 * @param array $post_args Array of allowed post args.
+	 * @param array $config    Array of theme-specific starter content configuration.
+	 */
+	$post_args = apply_filters( 'starter_content_allowed_post_args', array( 'thumbnail', 'page_template' ), $config );
+
 	$core_content = array(
 		'widgets' => array(
 			'text_business_info' => array( 'text', array(
@@ -2006,11 +2016,25 @@
 				}
 				break;
 
-			// Everything else should map at the next level.
-			default :
-				foreach( $config[ $type ] as $i => $item ) {
-					if ( is_array( $item ) ) {
-						$content[ $type ][ $i ] = $item;
+			// All that's left now are posts. Not a default case for the sake of clarity and future work.
+			case 'posts' :
+				foreach( $config[ $type ] as $id => $item ) {
+					// Posts and pages can be passed certain other args
+					if ( is_array( $item ) && ! empty( $core_content[ $type ] ) && ! empty( $core_content[ $type ][ $id ] ) ) {
+						$content[ $type ][ $id ] = $core_content[ $type ][ $id ];
+
+						foreach( $item as $key => $value ) {
+							if ( in_array( $key, $post_args ) ) {
+								// Some special cases where fields are really in meta
+								if ( 'thumbnail' === $key ) {
+									$content[ $type ][ $id ]['meta_input']['_thumbnail_id'] = $value;
+								} elseif ( 'page_template' === $key ) {
+									$content[ $type ][ $id ]['meta_input']['_wp_page_template'] = $value;
+								} else {
+									$content[ $type ][ $id ][ $key ] = $value;
+								}
+							}
+						}
 					} elseif ( is_string( $item ) && ! empty( $core_content[ $type ] ) && ! empty( $core_content[ $type ][ $item ] ) ) {
 						$content[ $type ][ $item ] = $core_content[ $type ][ $item ];
 					}