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> The coding by convention is rather for the /core part of Piwik.

It's not coding by convention if no one is supposed to use it. Then it's just an architecture; a way to organize ideas.

Events might work for an application that wants to be extensible in predefined areas. They can't be used to create framework/platform where anything is possible. What Piwik is and wants to be, however, remains to be seen.

Of course, Piwik at the moment isn't really a generic framework nor does it have a core engine so events have to be used in certain (if not most) cases. That doesn't mean they should always be or that using events is good practice.