Let's get the giant elephant in the room out of the way first.
There are only two ways in which TROS title would make sense:
- old Skywalker isn't dead
- Rey is the new Skywalker
Luke is dead. Bringing him back from the collapsing in the air cape visual Obiwanism would be the worst damage control ever. JJ is smarter than that.
Rey is not Luke's daughter. There was nothing between these two to suggest it in TLJ, wiggling it now would be the worst damage control ever. JJ is smarter than that.
So that leaves us with only one viable option - Rey, of currently no last name, will take on Skywalker family name. You know, being the closest to Jedi legacy. Plus it doesn't cancel out "Rey's parents are nobodies" imposter established canon. And it's going to be classic JJ's fob off one scene "deal with it" slap on - she'll come to Leia, say something like "I want to honour Luke, sob sob", to which unused-footage-Leia will reply "Take on his name, he liked you very much, he would love that" with her back to the camera. They hug. The entire old generation of cinema goers gasp "What? How? Who? Where did that come from?" and slap their forehead, but kind of go "ow right, better than Johnsonist crap anyway" inside. You know it's going to happen. No other explanation for the Skywalker title would be accepted as not forced.
Emperor laughter is only Rey's force flashback, like vision of Cloud City's internals in TFA. JJ clearly wanted her to be seer force user.
Kylo Ren will try to get Darth Vader's light sabre from the wreck of Death Star. That's why Rey is there.
