Yeah, I mean, I don't believe they are going to merge these zones into a single one. After all, for what we know for sure, is that we are returning to Quel'thalas - so the only thing that's safe to assume is that it's the only thing we get at the beginning, therefore no Lordaeron and so merging wouldn't make sense.
Personally, I'd loooove to see the entire Northern Lordaeron remade, with Quel'thalas being what you suggest in your comment, merged zones. My dream for 12.0 would be:
1. Eversong Woods + Ghostlands (with Silvermoon as a neutral capital city with Suramar-like vibes, connected to Quel'Danas with a huge bridge just for the sakes of visuals);
2. Lordaeron (Tirisfal + Plaguelands - with Arathi, Scarlet Crusade, Silver Hand and Turalyon plotlines);
3. Amani Lands (partially void-infected);
4. Isle of Quel'Danas as the endgame content with Corrupted Sunwell as the first raid;
Midnight fits
Light vs Void theme perfectly, so it's a great opportunity for the Army of the Light wet dream to come true
and since we know Sunwell could have served as a portal to summon Kil'jaedan, why not allow Turalyon to summon Yrel and her army through purified Sunwell for Renilash as a finale for 12.0 campaign