Again, the problem isn't whether or not somebody will write it. The problem lies in the fact that she can only be written once. Unlike the other characters, the PC's mom isn't something optional. You can't go around the universe collecting more "moms" or throw her into Tarkus' desert and forget about her because she's not your cup of tea. You'd be forced to accept whatever history is written about the PC and their mom. It removes from the player's experience, since you don't get a say in this. For example, wouldn't you be annoyed if they said that the PC has a pet cat, but they're not allowed to get another pet or remove the cat?You can say that about anything really - that somebody would have to write it. Obviously, if you were to introduce her as a persistent character, she would need to be extensively fleshed out like any other. But it would be worth it, she would add a lot to the game in terms of depth that most characters won't just because she is the MC's mother. That being said, I'm alright if nobody does it, but I would also be excited if somebody were to. And if they did I would prefer if they had an independent vision, left to their own devices creatively. That way the character would feel more organic and not just an assortment of the many wishes of the public of what we think she should be like. Besides the obvious, should she have the option of sex scenes or not, because this is a porn game after all.
edit: a pet cat on your ship, I mean