While having a WSJF score for each PI is useful, the main benefit of having a WSJF score for an epic is to have the ability to compare the value of each epic across the entire portfolio. You have to be able to see what your most valuable epic is, regardless of where it is currently planned. That is why I would like to have an 'overall epic WSJF' score that you could estimate with and show on the backlog view.

Currently you can only use the 'Estimate' functionality by PI. So you cannot compare things from your unassigned backlog against something in a PI. If an epic has changed WSJF from one PI to another, you may have something in your funnel that is more pressing that you should actually consider pulling forward and pivoting from the current epic. Because Align forces you to pick a PI to estimate an epic prevents that comparison across your entire portfolio. Align also removes the WSJF score from the Backlog view if you have a WSJF score for multiple PIs.