I don't know, like I certainly don't think it's impossible - but if Mattel's moved away from single-carded non-wrestlers, it feels like there has to be a reason; even Bloodline Heyman only got a 3-pack release (although in fairness they had to re-release him solo in one of their Oh I Guess People Still Want This Guy lines for Ringside, so maybe they're just being overly cautious at this point). Even the Main Event 2-pack line seemingly doesn't have managers show up anymore.
I don't know, I have to wonder if they got gun shy from a few examples like the Target Legends Heenan and Stacy Kiebler releases that reportedly pegwarmed in a lot of stores. When stuff like that does show up single-carded, it tends to be in Ringside lines now like that referee John Cone figure did.
The civilian-in-superhero line question is pretty interesting, because you're right, it hasn't been tried to any significant degree aside from the occasional MJ in Legends. Mattel at least has some sales data for non-wrestling personalities. Even if we disagree with their conclusions, they've sold these characters. (I guess we've got a number of MCU non-cape movie characters, but the recency boost for movie figures applies; movie wave stragglers getting clearanced out is no big thing.)