First they are going to tell you it is not in the proper format so I am going to help you with that as I was thinking the same thing on one aspect of this.
Second you already have a tab in Create a Message to add all guild members, but you must be given the notifier rights inside of your guild.
Third here is what the Proposal should look like for the others tho.
Proposal
Adding the option in Create a Message tab to add all on the Friends List or your Neighbors
Current System (if applicable)
The Current system only allows you to all guild members when creating a message.
Details
It works the same manner of creating a new message and just hitting the Add all guild members button, instead of having to add each individual manually. Understand you can see your friends and neighbors by putting at least 2 letters and you can scroll through the names, however it doesn't identify them until you hit add. So you have to write all the names down prior to writing the message.
Abuse Prevention
I believe the only possible abuse is someone continue to spam messages to other players
Visual Aids
I don't have any as still can't figure out how to add a photo.
Conclusion
Understand you can see your friends and neighbors by putting at least 2 letters and you can scroll through the names, however it doesn't identify them until you hit add. So you have to write all the names down prior to writing the message.