a concept snippet for WordPress plugin to ensure it always enqueues the latest available version of FontAwesome via BootstrapCDN. Makes use of jsDelivr API to find the latest version of FontAwesome.

tinyconcept.php

<?php

add_action( 'plugins_loaded', array( 'tinyConcept', 'init' ) );
register_activation_hook( __FILE__,  array( 'tinyConcept', 'activate' ) );
register_deactivation_hook( __FILE__,  array( 'tinyConcept', 'deactivate' ) );

class tinyConcept {
	private static $fontawesome = '4.2.0';
	// init plugin
	public static function init() {
		// get FA version from transient
		self::$fontawesome = self::get_fontawesome_version( self::$fontawesome, false );
		// hook into cron
		add_action( 'tinyconcept_daily', array( 'tinyConcept', 'get_fontawesome_version' ) );
		// enqueue FA style
		add_action( 'wp_enqueue_scripts', array( 'tinyConcept', 'style' ), 9 );
	}
	// get FA version from transient, if transient is empty and $fetch === true, get latest version via API
	private static function get_fontawesome_version( $current= false, $fetch = true ) {
		$version = get_transient('tinyconcept_fontawesome');
		if ( false === $version && true === $fetch ) {
			$response = wp_remote_get( 'http://api.jsdelivr.com/v1/bootstrap/libraries/font-awesome' );
			if ( !is_wp_error($response) ) {
				$response = wp_remote_retrieve_body( $response );
				if ( !is_wp_error($response) ) {
					$response = json_decode( $response, true );
					if ( isset( $response[0]['lastversion']) ) {
						$version = $response[0]['lastversion'];
						set_transient( 'tinyconcept_fontawesome', $version, DAY_IN_SECONDS + HOUR_IN_SECONDS );
					}
				}
			}
		}
		if ( 1 == version_compare( $version, $current) ) {
			$version = $version;
		} else {
			$version = $current;
		}
		$version = apply_filters( 'tinyconcept_fontawesome_version', $version );
		return $version;
	}
	// create WP-Cron hook on activation
	public static function activate() {
		wp_schedule_event( time(), 'daily', 'tinyconcept_daily' );
	}
	// remove WP-Cron hook on deactivation
	public static function deactivate() {
		wp_clear_scheduled_hook( 'tinyconcept_daily' );
	}
	// enqueue FA style via BootstrapCDN, protocol-agnostic.
	public static function style() {
		wp_register_style( 'font-awesome', '//netdna.bootstrapcdn.com/font-awesome/' . self::$fontawesome . '/css/font-awesome.css' );
		wp_enqueue_style( 'font-awesome' );
	}
}
?>

Highlights:

• it uses jsDelivr API to discover the latest version of FontAwesome. It is the recomended method by FontAwesome people [ https://github.com/FortAwesome/Font-Awesome/issues/3115 ];
• remote calls are made via WP Cron, not on the usual pageloads, to avoid affecting performance;
• latest version is stored in transient that has a higher expiration (25 hours) than the frequency of cron task (24 hours);
• if transient is not set, version defaults to the one that was hardcoded into the plugin;
• plugin provides a filter for the version number.