Why? We barely need the faction capitals right now. There is no need for race capitals. The new allied races barely have a home area.
The most possible way to get new versions of those cities is if they become useful and relevant in a future expansion. Then we can have a rebuilding scenario, probably pre-expansion, and then use them as capitals for the new story. But that's a longshot. And given the fact they already provide a past version of them through time magic, I think that's it for them. I guess we will see. But I can't see that happening during Shadowlands.
If they are so lame at Blizzard and just copy FFXIV now, there is a great chance we will get back after Shadowlands to find Azeroth destroyed somehow. And maybe those two forgotten cities will appear irrelevant to the new evil forces and not get assaulted. And if this happens, we can rebuild them and use them as secret new capitals for our factions.