There are 2 reasons you might justify sharding in a starter area:
- resource contention (quests and mobs to satisfy them)
player population load (sheer player count in a given area)
Whichever reason it is (and most would tell you it is quest mob contention), the plain fact is: anywhere else in the game world where that same type of issue would likely and regularly crop up, would warrant the same sharding treatment given that is why it was justified for the starter areas in the first place.
If new shard creation occurs at S+1 players in the starter areas, then it follows that Blizzard would also justify this happening in other parts of Azeroth that exhibit the same limits:
- if due to mob contention reasons, then anywhere else in Azeroth where an S+1 player bottleneck for mob or other finite required resources occurs, is grounds for that to also be sharded.
- if due to player population load reasons, then anywhere else in Azeroth where an S+1 local concentration of players occurs, is grounds for that to also be sharded.
The problem should be clear by now ... and the shard threshold S is the culprit.
This is the important point to grasp: If S = 100, then resource contention or population load > 100 anywhere quite literally justifies sharding as well. Remember, the starter areas with 2,000 to 3,000 players all at once may need 20 or 30 shard copies of size S, but even other areas that would have only 200 to 300 players would still warrant 2 or 3 shard copies of size S for the exact same justification. Whatever you pick S as, you have to be consistent and also split other places that exceed S for the same sort of resource contention of population load reasons.
This is very similar to the use of /pickzone in Everquest TLP servers. It isn't just Greater Faydark, Crushbone or Blackburrow (initial big hunting zones) that have many copies; zones all the way through max level like Lower Guk and Solusek B and Permafrost have many copies going as well, since they all generally split at the same max player value S. The fact that the lower-level places have more copies doesn't preclude the upper-level places from having > 1 copy.
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tl;dr
It does not matter that starting areas need 20 copies and some other area would warrant only 2 for the same sharding threshold limit S; that other area still warrants the split into those 2 copies according to the same rules that you used to split the starting area into 20. Are you not going to follow the same logic and split all these other cases too - and if you don't, why did you have to do it to the starting areas?
This is why I do not believe Blizzard will stop at starter areas.
No sharding at all is best, otherwise Blizzard will have to employ it in other places that suffer from the conditions they say cause the need for it even more than starter areas do, based on their simple mathematical claims. Otherwise it is pretty blatant hypocrisy to omit it in those other areas that scream even more loudly for it. Any area exceeding S even once would have to split to be consistent.