> And what I should do if I want Customer which can trigger events?

then ask yourself about the API of your customer
Do you want the full API of Announcer? I doubt.

> Do you think �"EventSource subclass: #Customer" make any difference? Or do you think we should never use inheritance to make domain announcer classes? What the existed alternative? I don't want always add announcer instance and couple equal methods any time I need it.

Think about API not about code reuse.
Think about polymorphic objects.
Each time you subclass from Announcer ALL the API should make sense.