Use "Date entered Deal Stage" in reports

It would be very helpful if you can make it possible to use the property “Entered Deal Stage” as a time/date point of data available to make reports with.

Our user case: we want to track “deals lost” after they were closed (lost customers), but we do not want to change the original close date (when it was closed won). This makes it very difficult then, to be able to track when we lost these customers. What I would like to see is a chart of "Deals entered Deal stage “Lost Customer”, broken down by month.

I would be very happy if you coudl consider enabling this fetaure, and Im sure many otehr companies would benefit from it! One of your support assistants advised me that you do have this date stamp data in the system, just that it is not available for reports creation.
Thanks in advance,

Fanny