'On this day' tool
Choose any date, and be presented with a list of all of the anniversaries occurring on that date.
As a list, this could be separated into sections for anniversaries of different levels of significance (10 years, 100 years etc), and ordered by event rank so that the most 'important' events are at the top of the list.
An alternative view would be direct display of the results on the timeline. A lovely extra would be colour coding them by the type of anniversary (e.g. centenaries could be set to red)
Note: this has been posted by Histropedia, but was originally requested by Harry Mitchell (https://en.wikipedia.org/wiki/User:HJ_Mitchell)