Nikki's history includes being molested by her father. That's why she became stripper. Her having a son and giving him up for adoption is plausible. but I think she would have looked for him and/or told her family about him.
Quote Axl Rose: I think Steve Burton's character, Avery's ex, Dylan McAvoy, he could be Nikki's son, a son Nikki had but never told anyone about, not even Victor, and that we hardly know anything about Nikki's past except that she came from a bad home, and she ended up becoming a stripper hence how she met Victor but what if before she ever met Victor, she could have had a child with someone before she met Victor and gave this child up for adoption because of the fact that she was a stripper and she could probably not afford to take care of a child at that time and Nikki could have had a child in that time frame before ever meeting Victor, and what if that child she gave birth to, was a baby boy, and Nikki gives him up for adoption and that child that son of hers turns out to be Avery's ex
Can you imagine the drama there, Nikki having a new son, but that son turns out to be Avery's ex and Nikki's other son Nick is dating Avery
And it gives Nick another brother, and it gives Victoria another brother too
Dylan would obviously be older than Nick and Victoria