Thinking about this, I don’t think we need the option at all.
Consider Inventory Value Movement report which already shows all inventory items even if they have no movement. The reason is so the total at the end of the report for opening and closing balances match the balance sheet.
I think Inventory Quantity Movement report should be consistent. In other words if Inventory Value Movement report shows inventory item, Inventory Quantity Movement should show it too.
The latest version (19.5.41) implements this now.