I think it'd be very useful if we could tag all users that replied in a topic - so that we can provide an update without being a best answer (which sometimes infuriates users due to the fact a bug may not be fixed at that point). Sometimes during the course of a bug, our devs need further details for the users being affected. In this case, a 'reply to all' mechanism would be an elegant an efficent way to reach out to everyone in a determined topic.
Should be relatively easy to implement, I assume 
