Echo of Gul'dan

Lot's of info about the fight here but not much regarding travel, so here's the quickest I found after the removal of Dalaran lower portals, without using toys and other travel tools.
Vision of Time - Oculeth will send you to Caverns of Time. Take the Zuldazar portal to Silithus and fly to Caverns (will change with re-introduction of Caverns portal soon).
Echo of Gul'dan - Hearth to new Dalaran, take Orgrimmar portal, then talk to [npc=150131] for portal to Blasted Lands.
Echo of Warlord Zaela - Head to Shattered Landing (72.73 49.44) in Blasted Lands for portal to Orgrimmar then to Pawdon Village from portal room. Fly rest of way.
Echo of Garrosh Hellscream - Hearth your way to Orgrimmar again (if both on cooldown can use Garrison or fly to Shrine in the Vale). Meet Anachronos outside gates of Org.
Restoring Old Bonds - Hearth back to Oculeth in Zuldazar. The travel hassle is done, so now it's just either enjoy or work through the rest of the chain (your choice lol). It's almost over and you can claim your new race and mount soon!

Edit: - As per grosicky & Catkind comments below (thx for reminders, wish I'd remembered before doing the chain lol), for Echo of Gul'dan & Echo of Warlord Zaela.
Note that the [npc=150131] can bug sometimes for some people and they won't port you to Blasted Lands, however thirstycow has listed a workaround as per below:

For any characters that have a bugged Thrallmar mage (2/12 of my characters have the issue), here is the quickest alternative option:
1. Use the Undercity portal on top of the Zeppelin towers
2. Use the Hellfire Peninsula portal in Undercity (right next to you after step 1)
3. Go through Dark Portal into Blasted Lands

If you need to use this workaround please head to [npc=150131] & throw an upvote on thirstycow for their work :)

Questline for [faction=941] (available when Ready for War completed and exalted at [faction=2157])

1. 
   
2. ([quest=49930])
3. 
   
4. A Choice of Allies
5. 
   
6. Vision of Time
7. 
   
8. Echo of Gul'dan
9. 
   
10. Echo of Warlord Zaela
11. 
    
12. Echo of Garrosh Hellscream
13. 
    
14. Restoring Old Bonds
15. 
    
16. Calling Out the Clans
17. 
    
18. Bonds Forged Through Battle
19. 
    
20. Tyranny of the Light
21. 
    
22. The Uncorrupted
23. 
    

You get Allied Races: Mag'har Orc and [item=161330].

Definitly not the easiest fight at the begining of the expansion :

Trick for caster : get to max range and you will dodge everything whithout too much issues.
If you don't decast the fear, you will still not take any damage if you are max range.
Also at max range, Gul'dan does not cast his filler, hence you avoid all direct unavoidable damage. He cannot move so you are safe.

Did this as a shadow priest and killed him without any problem after an attempt at mid range where I got wrecked.