He's now being nerfed in shadowlands, I'd say he is more on par with other leaders like Malf/Tyrande, Alleria etc, and with Sylvanas now at god like levesl of power and clearly having a different fate, the most awesome move for the forsaken would be leaders of the Undead scourge with a capital in Icecrown Citadel. Bolvar the Lich King their leader, and Calia Menethil, the sub-race leader for a lightforged undead allied race.
I would actually really like that. I thought Ice crown CItadel was an incredible city, and is perfect for tthe Forskaen to return to a faction level race. Why create or build a new city when Icecrown Citadel fits the bill perfectly? I would prefer it over using the Ruins of THeramore.
New Capital: Icecrown Citadel
Second base: Theramore ruins
SO I would make Theramore ruins the "Echo Isles" of the forsaken. Just like the Dark spears would likely be based in Zuldazar now, I think this is an exciting move for the forsaken, if they do it.