Hero's Call: Darkshore!

This quest is a Breadcrumb quest.

Breadcrumb quests are quests that, even though you did not complete them and they were available at some point, have become unavailable permanently after certain conditions were met. If this happens to you, and you're a completionist, this quest can be marked as excluded in the Wowhead quest tracker if you are no longer able to complete it.

• Your character is level 19 or higher, at which point this quest is replaced on the Hero's Call Board, by Hero's Call: Ashenvale!.
• 
  
• Breaking Waves of Change or Breaking Waves of Change (Worgen) is completed.
  This is a zone introductory quest leading to this zone. You can only complete this quest, or the zone introductory quest, not both. Completing the zone introductory quest will therefore make this quest unavailable.
• 
  
• The Last Wave of Survivors is completed.
  This is one of the quests available in the quest hub that this quest points to, and is also considered a follow-up to this quest. Completing this quest will make all zone introductory quests leading to this npc, including this one, unavailable.

Examples of Breadcrumb quests and conditions making them unavailable:

• Hero's call quests.
  They become unavailable if your character's level is too high, and the hero's call board sends you to a different npc/zone.
• 
  
• Zone introductory quests.
  This also includes hero's call quests. These quests are often started in a certain lower level zone, and they direct you to the next zone. If there are several of these, including the hero's call, directing you to the same zone/npc, completing one will mean the others become unavailable.
• 
  
• Quest hub introductory quests.
  These are quests that direct you to the next quest hub in a zone. If you've already completed the quests in that quest hub, the quest directing you to it may become unavailable.
• 
  
• Follow-up quests.
  These are uncommon, but still appear in older zones that have not been changed much in recent expansions. Sometimes a follow-up quest of quest X is available before you complete quest X. If you complete that follow-up quest and go back to the quest X giver, you may encounter the error 'You do not meet the requirements for that quest', leaving you unable to start it or turn it in.

Note: A quest being unavailable does not necessarily mean it's unavailable permanently. If you have not met the aforementioned conditions, and the quest is still unavailable, then you may have missed certain required quests that precede this one, or you do not meet the requirements in some other way. Always verify this before excluding this quest.

As of Patch 7.3.5 you can do two breadcrumb quests that lead you to Darkshore.

You have to keep the order to be able to do both.

1.Breaking Waves of Change (for every alliance race) or Breaking Waves of Change (for Worgen only)

2.Hero's Call: Darkshore! (can be found on every Hero's Call board)

I went to the general entry for the Hero's Board and found the comment that helped me. Keep in mind that I had not yet done The Last Wave of Survivors. The Hero's Board only shows three quests at a time but you can keep accepting them to see lower-level ones. As long as you have not done the subsequent quest that cuts you off from the breadcrumb. I think I had to accept 34 other quests before I could see this one. If you have an addon like All The Things, you should miss fewer quests like this. I hope this helps someone!