Designer should highlight required properties in properties panel - for example to mark them with different colour, or place '*' after their labels, if they are empty. It should be clear what properties should be filled in the time user is designing the process model, not just after validation. It would be also great to highlight nodes in the diagram that have some required properties still blank.
In addition, when the designer comes up, by default it would collapse all the properties except the core properties that are mandatory list expanded.
Internal Whiteboard: Beta Blocker → Blocker Not critical for Beta, but need to address for GA