Finn is a Solo (read the new comics-Han was married before the '77 movie to a woman of color), thus making Finn and Ren half-brothers.
I’ve heard the now canon comic-book piece about Solo’s other lady. It’s an interesting angle but I don’t think they would do that. It would shrink the universe further than it already has been. I think Finn is a Han Solo type character but in no way related. There was always kind of a rumor (maybe it’s canon, I dunno…I don’t know what is and is not) that Han Solo had been a Stormtrooper at some point and defected himself.
Rey is a Kenobi, not a Skywalker (maybe Obiwan’s granddaughter). I only say this because of the voices she hears during her flashback (but she also heard Yoda’s as well).
Another interesting thought that did occur to me as well. But I go back to what Kathleen Kennedy has said about the Sequel Trilogy. This is the continuing story of the Skywalker’s. Rey is either a closely secreted Solo/Skywalker or her father is the “myth” that she didn’t even know was real, until now…Luke.
Snoke is Darth Plageus.
Perhaps a Darth Plagueis-like character. But, given the fact that the story teams, including the screenwriters, seem to be only picking bits and pieces of the E.U. to use, I’m guessing he won’t be exclusively revealed to be DP. But out of all of your hypotheses, this one might be the most plausible. Someone at Comic Con even asked the panel (Kasdan/Abrams) about this and Kasdan acted like he misheard them ‘Darth Vegas?’.