It is a pretty big deal. What it essentially means is that you are completely exposed, if you pardon the pun.
And yes, absolutely everyone with basic IT skills has access to this data as it is shared across instances. All it takes is a couple minutes to deploy a docker image and boom, I'm somewhat of an admin myself.
The fact that this data is stored in plain is a major security and privacy issue that makes me rethink this platform.
Nope, it's an absolute nightmare. The post basically outlines how you could feasibly exploit data across a majority of the Lemmy network without much effort at all.
With a bit more effort you could also link the Lemmy accounts to the users email, as becoming an admin is as simple as hosting your own instance and getting users to join.
Boom you have a business case of profiling people on Lemmy and selling those profiles to advertisers, stalkers and perverts alike.