Proposed Modifications to register_meta()

meta.php

<?php
/**
 * Register meta key
 *
 * @since 3.3.0
 *
 * @param string $meta_type Type of meta
 * @param string $meta_key Meta key
 * @param string|array $sanitize_callback A function or method to call when sanitizing the value of $meta_key.
 * @param string|array $auth_callback Optional. A function or method to call when performing edit_post_meta, add_post_meta, and delete_post_meta capability checks.
 * @param array $args Arguments
 */
function register_meta( $meta_type, $meta_key, $sanitize_callback, $auth_callback = null, $args = array() ) {
	
	$defaults = array(
		'label'				=> '',
		'description'		=> '',
		'meta_format'		=> '', //short_text, long_text, date, datetime, color, image, number, select
		'meta_format_args'	=> array(),
		'default'			=> '',
		'public'			=> true
	);
	
	$protected = ( '_' == $meta_key[0] );
	if( $protected )
		$defaults[ 'public' ] = false;
	
	if( $meta_type == 'post' )
		$defaults[ 'post_type' ] = 'post';
	
	if( $meta_type == 'term' )
		$defaults[ 'taxonomy' ] = 'tag';
	
	$args = wp_parse_args( $args, $defaults );
	$args = (object) $args;
	
	if ( is_callable( $sanitize_callback ) )
		add_filter( "sanitize_{$meta_type}_meta_{$meta_key}", $sanitize_callback, 10, 3 );

	if ( empty( $auth_callback ) ) {
		if ( is_protected_meta( $meta_key, $meta_type ) )
			$auth_callback = '__return_false';
		else
			$auth_callback = '__return_true';
	}

	if ( is_callable( $auth_callback ) )
		add_filter( "auth_{$meta_type}_meta_{$meta_key}", $auth_callback, 10, 6 );
	
	//TODO: put the data about the meta into a global
}

?>