This feature request could be implemented together with #T100205.
The current text input field for dates and times could be replaced with a calendar widget / text field combination (I'm thinking of something similar to Django's standard form for timedate objects). This would help ensure that users input properly formated dates and that the dates they enter are really the dates that they're thinking of (i.e. typical date formating errors would automagically disappear, e.g. MMDDYY vs DDMMYY vs DDMMYYYY, etc.).
My idea of a super dooper widget would look lke this: Left a text field and right a calendar widget. The calendar widget could be used to select a date. On selection the date would appear in the text field (e.g. ISO formating). The user could edit the date at that point. Alternatively, the text field could be used to enter the date. If the date could be properly parsed, the calendar widget would refresh and show the date. If not, the text form could shake and highlight red or otherwise notify the user that the date could not be properly parsed. Improperly formated dates would lead to disabling the submission button until the date field was either empty or well formed.