Wasn't it Vanae: history codex not enitrely new race codex? Well afaik last time I looked at that stuff long ago it was about now long gone species, that evolved in today Vanae at Mhen'ga. They may exist somewhere in galaxy but I think Jim said, that he won't be writing content for meeting those aliens so per se, so we will never meet them in person and just learn about them from data founded during some quest/casual exploration of specific area/other way Jim set up for us to find it. That also makes quite interesting how in future this one codex entry will be treated. As without any actual aline it would be something like extended history section for Vanae. Well we'll live we'll see how devs will handle it when the time come ^^