I don’t think that it would be negative to the overall community of there was sharding for a few days after the initial launch, HOWEVER I seriously have no faith in Blizzard to not completely overdo it whenever there is the slightest bit of lag or complaining on the forums.
I play on a roleplay server. On roleplay servers there is “no sharding.” Supposedly at least.
The reason for this is that when the massive sharding hammer came down in Legion, it completely destroyed all of the big roleplay servers because it split up the community. So you might not run into your In-character friends because they are in a different shard. So, Blizzard removed sharding from capital cities after the Legion launch, but left it active in the open world.
This was still a problem though, because roleplay servers (particularly moonguard) have massive events out in the world where hundreds (sometimes even into the thousands) of roleplayers come out into the open world. Half of one of these events (Tournament of the Ages) was ruined because those thousands of attendees turned into dozens because of sharding. From then on, Blizzard promised that sharding would be removed from all roleplay servers entirely.
Now we come to today. For the most part, they have kept their word, but they have slightly changed their word too. Now, during certain events, like expansion/patch launches, and the like, sharding is enabled. Except that isn’t entirely true. As recently as a few weeks ago I was having to invite friends in order to get them into my shard IN CITIES on RP servers. No expansion launch, no patch, no events. So either Blizzard flipped the switch for some reason and turned sharding on for a short while, or it is a system that automatically activates sharding once lag reaches a certain threshold. Or something. Nobody knows.
I don’t want this for classic. I don’t want the “ohp here’s sharding all of the sudden with no warning because we think it needs to happen but we aren’t going to tell you why or how long it will be active” that we have on roleplay servers when I’m playing classic. Blizzard have only said that they are considering sharding as a solution for on-launch lag. But they haven’t explicitly stated whether or not it will be used in the future for large scale events, or just if the servers get too laggy again. I don’t trust them to keep the sharding to an acceptable level that wouldn’t SEVERELY hurt the classic community.
TL;DR: I am extremely apprehensive about sharding. Not because I think it being active for a few days after launch would destroy the community, but because I don’t trust Blizzard to keep the sharding deactivated permanently past that point.