I think indicator-datetime as main mate component should never depend on an external application like evolution because :
- Evolution is not the only one used on Ubuntu and most people use e-mail or tasks on browsers.
- When someone tries to remove Evolution also indicator-datetime is removed, this is not logical dependency, and the natural is that indicator-datetime should remain showing date and time while disabling features related to evolution.
- If someday Evolution is abandoned, what will happen to indicator-datetime ? should we develop another one that depends on another evolution-like app ?
- If Evolution modify any api the change should also projected on indicator-datetime, this creates an asynchronous relationship.
I think the new indicator-datetime should remain simple component that displays only date/calendar and time and should never depend on any external library.
And what should be done is to develop an indicator specific/integrated to/with Evolution that facilitate the access to its events, tasks, mails ...