[@Vec] if I remember the contents of this thread correctly, adding users to a 'players' group for each RP has been suggested before, as part of the more advanced GM tools, but I'd imagine that is a long way off. That system would be a prerequisite to what you are asking. Otherwise, as [@NuttsnBolts] said, the closest thing we have is Subscriptions sending notifications whenever a new post is made. Sending an extra notification via the Subscriptions system might be superfluous.

Although, perhaps it could still be used. Regular Subscriptions notifications just get bundled up into 'unread posts'. You already get additional notifications if someone in a subscribed thread quotes or mentions you. So a possible feature is: When a GM/Co-GM makes a post, perhaps they could have the option to flag it as an announcement, which tells the Subscriptions system to send an additional notification to ensure that people checking their notifications notice that an announcement has been made and it doesn't get lost among other posts.

Although, that might be more effort than its worth to implement, especially if it's really just a patch until a more advanced system can be put into place.