I don't understand this remark. If we want to use such a signal we have two places where to set the default values of the variables: Either we set them before sending the signal (which is done to manipulate a given context dictionary) or we (and all other developers of plugins) have to care about this like:
```python
context.setdefault('extra_stuff', [])
context['extra_stuff'].append(my_additional_extra_stuff)
```
I prefer the first solution because we (the core devs) can easily control where the signal is sent. These are only some places (ExtraContextMixin, VersionView and ErrorView) and they are less then the others ones, I think.