This would be enormously helpful for us. We use attributes for so many things - e.g., the year a politician was elected; the year a teacher began at a school. The date field is more or less wasted in a case like this when we do not have an exact date, but we do have a year.
YES PLEASE!
We currently have to add an additional "former" attribute/custom field for certain attributes that require and "end date".
For historical purposes, having this is important.
This feature would also be enormously helpful for my org, as we track diagnosis and referrral dates which are sometimes only a month and a year.