The reveal that Rey is a Skywalker or Solo is also what everyone is waiting for, so it's not necessarily the sort of things you want the audience to anticipate for two years, with the expected big "duh" effect at the arrival line.
Abrams gave people what they wanted with Episode VII. I feel that it's the arc that the audience wants, and that even if that wasn't the original plan, they may divert to it. Just as in the original trilogy Lucas made changes on the fly, so can Abrams and co.
Because there's still questions (who left Rey, who is the mother, etc) the audience still has things to look forward to.
We know that Snoke had interest in Ben from early on. That's why Leia sent him to train with Luke. If Snoke was unaware of Rey, that's a reason to keep her hidden. Just as Palpatine would be interested in offspring of Anakin, Snoke would be interested in more Skywalker blood.
If Luke left her, it could be because he was unconvinced he could prevent a fall to the Dark Side as he was unable to prevent with Ben. He needed to learn more before he could teach again.
In the last case, Rey is most likely a "padawan', a survivor of Kylo's attack on Luke's academy, and the person who left her there was possibly already being hunted down by the the Knights of Ren. Stopping to dump her on Jakku was a last resort, her only chance of survival before Kylo caught up with her guardian's ship. If by a miracle the guardian escaped, he/she could return soon for Rey... which didn't happen.
If Rey was abandoned, we have to look for people who aren't necessarily evil, but at least rather selfish: after what happened at the academy, they didn't want a child with force sensitivity and they dumped her. Not the most likely scenario. Or maybe they hated Jedi, but couldn't bring themselves to kill a young child. Not too likely either.
The "Jedi trainee" scenario is probably the most likely of all. It turns the story of Kylo into a personal tragedy for Rey since his actions against Luke also pretty much destroyed her life, and creates a connection to Luke without a blood tie. It might spark a conflict if Luke decides at first that Rey shouldn't be trained, especially not if it's to take revenge on Kylo. If no one but Kylo knows what happened to Rey's saviour/guardian, her inner conflict also remains unresolved, until/unless Kylo makes the big revelation to her that he killed her parent/guardian and thought her dead.
That scenario is certainly possible in the light of the novelization. There's this scene during the duel when Kylo seems to realize who Rey might be, but Rey doesn't recognize him (as she might a close relative). The same novelization makes some of your scenarios extremely unlikely, as we have Leia's thoughts on Kylo's history, what she kept from Han about him, what lead to Luke vanishing and Han and her to split up. Nowhere in there is a hint of a second family tragedy involving a little girl. It could be a cheat, but it would be a really big one. It at least rule out any possibility that Rey is a solo child thought to have died or disappeared from Kylo's attack on the Academy. That tragedy would be as great to Leia and Han as losing Ben, and it's not possible Leia would have made complete abstraction of it while thinking about the events surrounding Ben's turn to the dark side.
Nothing in this scenario prevents her from being Luke's daughter.
A big problem with her being a Solo or Skywalker is also her age. She was born many years (maybe 5 or even close to 10) before Ben turned to the Dark Side and the coming in the open of the First Order. It's very hard to see why her existence would have been kept a secret at the time while Ben's wasn't. That leaves only the possibility that even Luke doesn't know she's his daughter, but why wouldn't he? I don't find it so likely that Luke had an illegitimate daughter he never knew about, and even less that the mother or guardian would after he vanished think it's suddenly a good idea to dump the child alone on a junkyard planet...
See above. Snoke knew about Ben, and had interest in him. Leia sent him to train with Luke because she already sensed the Dark Side within him. Hiding her from Snoke was the goal.
Not only this would be an horrible thing for Luke to do, but why would he think a young child would be safer there on her own han with him, who intended to disappear?
Because he was afraid she'd fall to the Dark Side. Luke (as far as we know) never received full Jedi training. That's where he's gone.
This sounds very unlikely, unless the mother escaped from the academy with the Knights of Ren on her heels and she had no choice but to dump the child somewhere before they caught up with her... but why in such a scenario would Leia not know about her niece being missing or dead and not even think of this when she outlined the reasons why Luke vanished (in the novel)?
Why would Leia know about a niece if Luke doesn't even know about his own daughter?
Also, she could just be an illegitimate daughter, who was never at the academy. Maybe her mother was on the run from other people. This option leaves a ton of possibilities.
This is the option that makes the least sense. Why would Leia abandon her daughter on her own on Jakku, when she or Han have this vast network of contacts to make her disappear "safely", not to mention she'd probably be safest with either of them, especially Leia!
I agree, but it is a possibility.
That doesn't work if she's a Skywalker or Solo, for some of the reasons above, and for the fact this, not Kylo's turn to the dark side would be the big tragedy for Luke. There's also the problem that Luke or Leia could probably sense if their daughter had died or not.
It makes a ton of sense if she's a Skywalker. Killing others is one thing, killing your own blood is something else. That's why when Ben kills Han, it means so much: he wasn't able to do that earlier with Rey.
The most likely option, but this works much better if Rey isn't a Solo or Skywalker, and thus just another victim of Ben, not a personal tragedy in Luke's or Leia's life that it makes little sense not to ever mention even in the movie, and it's even more difficult to accept in the novelization where we get Leia's thoughts and Han's on the back story.... that's something HUGE to leave out, a massive cheat.
True, but it still works if she's Luke's daughter.
I have to disagree. As above, the fans want her to be a Solo or Skywalker. Abrams will have learned from Lucas' mistakes with the prequels.
Also, if she's something new, why the visions with the lightsaber? I think it's because her strong connection to Luke and Anakin.