EXT: FORM - For date fields placeholder the date format is used instead of a dedicated placeholder value
When adding a field of type date, there is no option to add a specific placeholder value as you can do in other field types. Thus the date format is taken as a fallback for the placeholder (according to the datePickerViewhelper). As the date format is a PHP based one, a regular website user probably gets confused having a format such as "d.m.Y". So a dedicate placeholder info would be best to serve a sample date or a end user readable format.