This feature could be done by adding an allarm on the icalendar file and then subscribe as explain in http://www.projectpier.org/node/1369.
I think that could be done by adding a code like this:
BEGIN:VEVENT (or VTODO)
DESCRIPTION:bla bla bla
END:VEVENT (or VTODO)
for every event(milestone) or to-do (task) generated in the ical file/link submitted by application/controllers/FeedController.class.php (I have select a 'one day before' allarm, but it can be different or may be choose in some other way Full spec: http://www.kanzaki.com/docs/ical/valarm.html)
In library/icalendar there are all the specification and the classes of ical generated file. What is missing is the render function and the validation of the component VALARM as a sub-component of VEVENT or VTODO.
I think that component could be a part of the generation of VEVENT or VTODO, but what I can't find is where 'BEGIN' and 'END' of this componet could place. Another problem for me is the validation, because it could be done with a new class definition of VALARM component or added as valid property in the existing class of VEVENT/VTODO.
The VALARM support email notifications too...