Custom Metaboxes and Fields (CMB) will create metaboxes and forms with custom fields that will blow your mind. This is version 2.0 and has been completely rewritten.
cmb2/js/cmb2.js
and edit line 499, changing $table.find('.cmb-repeatable-grouping').last();
to '$table.find('.cmb-repeatable-grouping').first();' and edit line 508. changing $oldRow.after( $newRow );
into $oldRow.before( $newRow );
it will do what you want. However you would probably want more to make sure the page scrolls to the new row. Also this will not affect how the rows load from the server.