Yes that was exactly what i told you, if they support a new fork or just another update, they will let you know by email.
Just like it happened with bticoin gold, they supported it, and one day before it, they sent an email to all coinbase users that they were going to give out bitcoin goldies to all bitcoin holders.
And that is how it works, they are the only ones to decide which coin are they going to support or not
But you are right, they could have a note in there, but it is coinbase.. people will still be using this wallet because it is the more easy to use, and the most famous one