I'm looking for ways to integrate custom invoicing into MarketPress. I find it strange that $this->order_notification is called before 'mp_new_order'. If I want to add custom metadata to the order, it is also likely I want to use that data when sending out notification.
Putting my custom invoice data structure handling into email notification filters just doesn't seem good programming, even though I could do that. I am not seeing any drawbacks for switching the order of those two calls, though. What do you think, Aaron, something for 2.6.1?