FacetWP – using the facetwp_indexer_post_facet filter

<?php

function lh_fwp_index_coming_soon_facet( $return, $params ) {
    $facet_params = $params['defaults'];
    if ( 'cf/edd_coming_soon' == $facet_params['facet_source'] ) {
        $value = get_post_meta( $facet_params['post_id'], 'edd_coming_soon', true );
        $value = empty( $value ) ? 'Available' : 'Coming Soon';
        $facet_params['facet_value'] = $value;
        $facet_params['facet_display_value'] = $value;
        FWP()->indexer->index_row( $facet_params );
        return true; // we're done indexing this facet
    }
    return $return;
}
add_filter( 'facetwp_indexer_post_facet', 'lh_fwp_index_coming_soon_facet', 10, 2 );