Heritage questlines are more about celebrating old lore. Whereas what future racial storylines in revamped zones might do, and indeed should do, is introduce the races to new players.
It's not easy for a new player to know the first thing about the Forsaken for instance. You have the opening blurb, and the basic stuff that you can glean from the starting levelling. But for one that isn't even an option for new players. And secondly it's massively outdated.
All races should get some quests that explain what they are. What motivations guide them generally. And what you should expect from them in the future.
In the case of Forsaken. What makes them undead, and why they get raised. What Forsaken society looks like. And showing stuff like Forsaken trying to make new settlements.