For pvp tourneys, I voted yes to allowing shards, but I think whether or not to ban them is really more a point of setting the feel of the tournament theme.
I think there will be a lot of times when banning them makes sense but it shouldn't necessarily be a default since tourneys are all about setting up new and interesting scenarios for deck building.
I do agree with some of the previous posts, that there are shards in need of balancing work. Putting them into their own elements has certainly helped a lot but it does suck for players that are just starting out when a rare and hard to get card is too powerful.
For that reason, its hard to put a simple yes or no for tourneys.
Tournaments aimed at pulling in relatively new players should probably keep shards banned. Tournaments aimed at veteran players, whom have had enough time to both collect shards and see them in action, can probably allow them in.
Lastly, I think that some shards are relatively balanced and innocuous, so why ban those in a blanket ban (i.e. SoSe, SoG)? Just ban ones that disrupt tournament meta.