"Players have no effect other than capturing or killing what they find."There's further clarification that the spawning is dependent on realm conditions and not the player.
While I'm glad for the confirmation either way, it still leaves us with very little to go on. On top of that, now that we know we cannot initiate the right conditions for it to spawn, that means we have to rely purely on luck. If we happen to find any Unborn Val'kyr up, every little detail of the time, day, environment, etc. will have to be noted to try and pin point exactly what on the server triggered the spawn.
It's pretty frustrating when you think about it. We're going to have to contend with RNG and possibly CRZ, and on top of that, we're going in completely blind. The only hint we have to go on is that it's a "new spawn mechanic", which could mean anything. Other pets that have specific spawning conditions at least give us hints as to what is necessary to find them. Winter for the Snowy Owl, Rain for the Baby Ape, etc. The lack of knowledge about the Unborn Val'kyr is fairly irritating.
I was excited to try and find out what the spawn mechanic would be for this pet, but only when I was under the impression that I could play a part in its spawning. My interest was piqued, and I was actually enjoying trying to brainstorm what I could do next to try and force a spawn. Now that I know I'm just going to have be 100% lucky, it doesn't seem as fun anymore. My role in this is purely random which is kind of discouraging.
So there you go. In the beginning it will be completely based on RNG until more people find the Unborn Val'kyr, take down notes on the conditions at the time and compare notes to determine the common factors and possibly the exact reason it spawned. Good luck to everyone, and seriously, may the RNG gods smile on pet collectors.