Totally agree this is a good idea, and one we have also seen a few times in the past.
As mentioned in another idea, we do have the ability to add multiple customers to incidents, and while this will allow you inform customers of major issues it feels like the wrong place to announce any upcoming changes to a service, adding similar functionality to Messages would be the appropriate place for this.
The "Notify Customers" functionality that is already in Knowledge Articles only applies to customers who have subscribed to the Knowledge Article's watchlist via the Portal.
