Hi Wantti,
I am not sure you posted in the desired section, as I don't think this a product evolution is really needed. In What you are asking can be achieved in several ways, depending on your implementation.
If you are using elasticubes, then you can just add a calculated rank of month in your data model. Your filter will only select the top X month, that will only depend on your actual data.
With Live connection you will probably want to find an optimal way depending on your database, and how the data are updated in the source database.
Ultimately you can also have a dynamic calculation of the month difference between two dates in your dashboard using a dashboard formula and then filtering on the result of this calculculation. You can also probably do this with an advanced JAQL filter, but probably more complex.
Hope this helps !
Best, David.