Potentially something in the Personal Cooldowns that tells you how many more minutes you have left until the next 10% energy refill. It would definitely be useful to track the next energy refill for the July event without using up the 10% during a battle in the Veiled Nebula.

Check out these other Suggestion threads too if you feel like it:
-Inbox Mass Deletion Confirmation
-Sales Chat Updates
-Collapsible Clans menu
-TC Blacklist/Exclusion + Only Frozen
-Hoard: Filter by event