This is the latest official word we’ve seen on it:
From Pazorax, Lead Software Engineer:
[Q: What are plans for phase 2 if some realms are horrifically overpopulated at 50K+ players? Will layering stay? ] https://old.reddit.com/r/classicwow/comments/ct08c7/welcome_to_the_rclassicwow_subreddit_ama_with_the/exi3y2l/?context=3
A: We’re absolutely committed to reaching one layer per realm by Phase 2.
From this post after the AMA via Kaivax:
Sorry the formatting is weird… it’s due to my trust level not being high enough.