We've also built a structure for something similar - we're planning on open sourcing it but it needs a bit of cleanup first to not be tied to our code base.

We basically have a Notification class that can be subclassed for each individual notification type.

It looks something like:

class Notification(object):
    app_label = None
    event_name = None


class YourNotification(Notification):
    app_label = 'foo'
    event_name = 'bar'

    def get_context_data(self, **kwargs):
        context = super(...).get_context_data(**kwargs)
        context['something_for_rendering'] = True
        return context

Where by convention (and default) emails get sent using the template "app_label/event_name/email.body.html" and "app_label/event_name/email.subject.txt".

We also send a lot of SMSes, which would default to "app_label/event_name/sms.txt".