Some players have found a way to get their friends across shards to join in on events and other things. This has led to a lot of claims that this is an "exploit," but is it?

I was actually in the same boat as many, feeling that it is. As soon as I found out about this, it appeared to be an obvious exploit. But it's actually not. In fact, this is a quote from Daglar himself:

Unintended but not an exploit.

We are actually going to be leaving these abilities on over the weekend until we see something horrifically breaks.

One of our longer term goals was to be able to fully support something like this, via UI, allow trading, etc - but 2.2 wasn't the intended time

After reading this statement, a player voiced a concern over zone events (such as the Volan event), to which it was stated that even if there were issues with the event, it would not be enough to disable the cross-shard functionality. The only things that are going to get this disabled are major problems (such as missing items/characters) or exploits. So for now, enjoy this new ability, and look forward to what all it might bring (such as a single shard in the future)!