Anyone implemented a solution on SharePoint 2013 were by an email is sent to the last person who modified a document >X days?

We are trying to tidy up our document storage when we move to SharePoint 2013. We can't use the document retention solution (we don't believe) because some docs need to stay for long periods of time and some don't.

We started thinking we could have a reusable workflow to do it as we don't want to add any columns to the document library (using calculated fields to add X days to the modified date) and we could then attach that workflow to every document library.

Essentially if a document isn't modified for 90 days it emails the person to say "should this be on here" 

Any best practices out there?