Where in the world did you get that idea??? Blizzard’s content plan was to remove layering by phase 2. This had nothing to do with server populations at all.
“We’re absolutely committed to reaching one layer per realm by Phase 2.”
“With hotfixes that we are currently deploying to all WoW Classic realms, we are substantially increasing the number of players that can be simultaneously logged in and playing.”
And that increase came after they said this:
“Please also note that our realm population estimates of Low, Medium, High, and Full are based on this increased capacity – a Medium realm today already has more characters on it than even the most crowded realms did back in 2006.”