Episode VIII updated role list
Who the bloodly hell is Nuke Skywalker!?
There are a couple of theories on who this guy could be. First off i find it unlikely that he is another son of Anakin. But maybe a son of Luke.
Let's play with that thought. Could he be dead?, or exiled himself after the Knights of Ren attacked Luke's Jedi Order. Which could also play into him being dead, and he plays his role in a flash back.
Could Luke have an offspring? If we look at old Jedi values from the time of the Galactic Republic and old Republic, then it the Jedi code would forbid it. Though there have been instances where this rule was ignored. Jedi Master Ki-Adi-Mundi was a Jedi who had a lot of offspring, this was tied into the low birth rate of his home planet.
Could Luke have gone a same route to secure the Jedi's survival? and creating more powerful force users, because of his powerful lineage. I find this very likely, especially because the Old Jedi Order was wrong and blinded by their ways, ignoring emotions in fear of it getting the better of them. It was Luke's compassion towards his farther that actually saved Vader. Also it was the Jedi's narrow minded view that also lead to Anakin's downfall. So i think it's possible that Luke took a much larger view on the Jedi order, knowing that emotions doesn't necessarily lead to the darkside. This view is also what defines Luke's New Jedi Order in the Expanded Universe.
Other possibilities, it could be a young Luke in a flash back and the name "Nuke" is just to throw us off, they are however pretty similar. Another theory i heard is that it's a clone (i hope not, unless it's handled very well).
Personally i hope it's Luke's son and that he's alive. Especially if Rey isn't a "real" Skywalker. Then they could mate and a new generation of Skywalkers could see the day of light.