Replace bubbles that send no ID

Not sure if this is a great idea or a terrible idea. Should replacing be opt-in or opt-out?

What I mean is, if you're an app developer and your app sends a notification: should you have to opt-out of replacing previous notifications by supplying a unique ID or should notifications only be replaced if you opt-in by supplying the same ID?

Currently, we create a random ID based on notification spawn time if the ID is null, but we could instead use the app ID as a fallback