
Xaela-as-dark-knight is explored in the job questline (or is Sid a Raen?). It's vague enough to think that more than one person could have experienced similar things and chosen a similar path.
On the topic of being a Dark Knight, though, it's worth keeping in mind that 1) they're an Ishgardian faction primarily, with their self-appointed roles keeping them, if not actually in Ishgard, operating against Ishgardian corruption and 2) the job's an enemy of the country, since they're murdering those with influence.
We don't know exactly where they shake out after the 3.0 MSQ resolves, but for the time being it's still something to tread lightly about.
On the topic of being a Dark Knight, though, it's worth keeping in mind that 1) they're an Ishgardian faction primarily, with their self-appointed roles keeping them, if not actually in Ishgard, operating against Ishgardian corruption and 2) the job's an enemy of the country, since they're murdering those with influence.
We don't know exactly where they shake out after the 3.0 MSQ resolves, but for the time being it's still something to tread lightly about.