We use built in portfolio item/epic fields and custom fields to categorize epics for different things. Currently from the Product Backlog and Storyboard we can filter on Epics themselves and see all the stories for those epic. It would be nice to also be able to filter on Epic fields, so like every epic that has Epic Source = X or Epic Strategic Theme = Y, and show all those stories that belong to those in the Backlog and especially on the Storyboard views.