This seems like a good approach, although it still presents some challenges, users create a list, kind30000, this list can have a special title, or a specific 'l' tag for example to make it easy to find. Then when someone wants to publish and send notification, it fetches all the lists where its pubkey is included and sends a dm to these users. Of course, for example, another approach could be client side, without the author who publishes having to do anything. It could be a client where users create these lists of people they follow and don't want to miss anything, this client could be designed for this purpose and focus on this.
Another idea could be to create an npub for an application that creates lists of subscribers, and people can sign up to that list, the flow would be that users access this app to subscribe to some lists, these lists are published by the npub of the application (so that it is possible to sign up individually to a common list) and then the user who publishes can choose to send a message to everyone on the list.

Just throwing out some ideas, however they could be further developed and polished.
In any case, I think it's a great use case!🔥🔥