this feature would be very interesting for me too.
Are there any plans? Or does any plugin do this job?
Just Place this on your template files or header file or where you want to display it
<?php if ( is_user_logged_in() ) : ?>
<a href="<?php echo bp_core_get_user_domain(bp_loggedin_user_id()) ?>messages/" title="Messages" data-toggle="tooltip" >
<i class="fa fa-envelope-open-o" aria-hidden="true"></i> //Font Awesome if you want the envelope icon
<?php echo bp_get_total_unread_messages_count( bp_loggedin_user_id() ) ?>
</a>
<?php endif ; ?>