Wikidata is something that has been eagerly awaited. Given that Wikipedia has articles on many events, it is obvious that Wikidata is one place where assertions on these events should end up.
The most obvious dates are the date of birth or death for a person or the date a ruler started his rule end, the date it ended.
There are many issues that I can think off about how dates are to be used. But the fact that dates are finally being tested and are likely to arrive in a weeks time is a reason to be happy.