With the update of Microblog 5.0 standard macros of Confluence are no longer usable natively. Thus also the Datepicker macro.
In the Mircoblog this macro is often used and I hope that it will be available again.
Samuel Lerch
Just in addition: I am interested in your use-cases of the date picker. What is the advantage of the Datepicker in comparison to the normal writing of a date? Is it Autocompletion or sth else?