I see sharding as a different issue from CRZ - cross realm zones artificially increase the pop of a dead zone by combining servers. This ends up having the opposite effect, where the game feels less social. Terrible feature overall. Just a bad idea, should be killed with fire.

Sharding in specific places could help the game a lot. On release day, sharding just the starting area could keep the servers from crashing and let you actually do quests. If sharding was used in places like the opening of the gates of AQ, that event might actually go smoothly. Anywhere else would make the game worse though, possibly preventing large events like a big southshore vs tarren mill brawl.

I'm guessing Blizzard already has an opinion on this though, and we'll see what that is in the demo.