Feature request

Agreed. I need to think about the implementation: if one wants to exclude tags in one or more categories, that would mean that tags that belong to two or more categories would be excluded, too.

I did some code that will get tags based on category, with exclude option, only problem is the query is to heavy for the database to execute everytime someone visits a page.

Perhaps you can use this code and optimize it into your plugin and make something good out of it.

$exclude_these_term_ids = array(1,2,3);
$custom_query = new WP_Query('posts_per_page=-1&category_name=technology');
if ($custom_query->have_posts()) :
	while ($custom_query->have_posts()) : $custom_query->the_post();
		$posttags = get_the_tags();
		if ($posttags) {
			foreach($posttags as $tag) {
 if (!in_array($tag->term_id, $exclude_these_term_ids)) {
				$all_tags[] = $tag->term_id;
			}
		}
}
	endwhile;
endif;

$tags_arr = array_unique($all_tags);
$tags_str = implode(",", $tags_arr);

$args = array(
'smallest'  => 11,
'largest'   => 11,
'unit'      => 'px',
'number'    => 10,
'orderby' => 'count',
'order' => 'DESC',
'format'    => 'list',
'include'   => $tags_str,
);
wp_tag_cloud($args);

This will display 10 most popular tags from category “technology” and exclude tags with ID 1,2,3.

IF you could figure out a way to accomplish the same thing but not load the database so heavily let me know!