Hasn't Matalas all but admitted that Ro Laren is returning?
I mean, he said it's a recurring character from TNG, but no O'Brien. Who else could it be who's still alive and not already been used?
The only reason I'm starting to wonder if it's actually Ro is because Matalas refers to this character as a "deep cut". Ro was a really well-liked recurring character, enough so that she got a whole episode devoted to her departure, so I'm not sure if she could be considered that deep a cut. If we're going for "obscure, but still impactful", maybe someone like Sito Jaxa? She appeared in a couple of eps, the writers were always hoping to eventually show she survived, but it just never panned out.