Yes, this justification applies equally to a client alert/notification system.
It does not, because a message displayed on your screen commanding urgent and immediate action does not provide a timeframe for public review and communication to take place.
But this is my point. This depends entirely upon what message is displayed, and how it is displayed. There are good ways of doing notification, and bad ways.
What you've described above is not what I have said in my posts on this topic. I agree I don't want a notification "commanding urgent and immediate action". But I do still think notifications have their place.
Multisignature is better described as semi-decentralised.
It depends on a trusted authority, the that the authority is a (perhaps informal) corporation rather than a natural person doesn't change the fact that such a system has a fixed center.
I don't understand what you mean when you refer to a singular "trusted authority". A multisignature system could be setup where you have a 5-of-10, or even a 20-of-30 (or any you consider appropriate), where a set of developers are able to issue notification. The notification multisignature system would be built into the client-release, and should be similar in working to the current development consensus building. In such a system a large number of qualified individuals would form an agreement, directly related to the work that they were carrying out.
If you're referring to the actual notification being the "trusted authority", again, I think that this is based on a very narrow assumption that the notification will be written and presented in a certain way. There are many different ways to write and present notifications.
Promotes Centralization - NACK
Please have the courtesy to actually read some previous posts on this topic before putting in a low effort comment like that.
A well designed notification system does not necessarily promote centralisation.