I have found a similar topic in US forums, and I will like to copy the idea here to show my support.
Soon we will have an expansion centered on Dragons, including Wrathion, a character who was a key role in the story of Pandaria expansion, but all the content about him was available on the MOP legendary questline.
With the removal of that quest chain, now is almost impossible to understand part of Wrathion backstory, not his involvement with Pandaria. Even Garrosh, the main villain of the expansion, involvement is easy to miss for new players due to most of the interactions of that character happening during that removed questline.
It was a mistake for Blizzard to remove the quest chain. It leaves a deep Hole of nonsense in the Lore. It is wrong that players must find youtube videos about a removed quest chain to understand the story of an expansion of the game.
That is why Blizzard should bring back the quest chain, allowing, for example, people to play the quest chain during Pandaria Timewalking. Just the same as Mage Tower in Legion Timewalking.
And what about the people who earn their rewards back them? Well, I don’t care about the rewards. Blizzard could keep titles, FOS, mounts, and legendaries exclusive for those who did it back in Pandaria and only bring back the original story, maybe with a new achievement that could be retroactively granted to old players or new rewards at all. I don’t care., I just want to play that quest chain again.
Legion Mage Tower is a great in-between solution. Keep original rewards exclusive, and bring back the content with new rewards.
And if they do that with MOP they could do the same with WOD Legendary Quest Chain.