If Blizzard do use sharding for the first few starter zones do you think it will stop there? Of course not, Blizzard lie and lie a lot, they would use it every time a lot of people are in one area. Blizzard cloud servers cannot handle any amount of people in one area, just look at BfA and how bad it is with ability and loot lag.
What is to stop Blizzard using sharding at events like the opening of AQ gates or the release of Naxx etc People need to really think before they ask for something.
Sharding and CRZ is why i stopped playing BfA, it’s gone overboard and killed my enjoyment for the game, it’s killed server communities and having sharding in Classic isn’t authentic.