Because things surrounding the franchise have become a bit blurry, it's hard to make a judgement call on how they'll close it out. Is IX to be the end of the saga films? At some point if you start going up to to like Episode 18... things almost become a caricature of themselves (Jaws 19 from Back to the Future anyone?) and kinda silly.
From that perspective alone, I'd be happy with 9 being the end of the Skywalker Saga and this iteration of the Chosen One prophecy (and I say that because who's to say what other prophecies had been made).
They just need to be sure to explain the concept of "Balance" better. Ie, how 10K Jedi and two Sith in hiding is balance. And if it wasn't, and if that's why the Sith rose to power (ie via Jedi's arrogance and hubris)... then was the millennia prior to TPM considered to be "in balance"? Cause that's a long period, and clearly the denizens of the galaxy believed that peace to be a good thing (re: Sio Bibble's comments about there not being a full scale war since the beginning of the republic).
I'm fine with Rey not being explicitly related to anyone. I do think it'd be interesting if she were implicitly related to the Skywalker line in that she, like Anakin, could also be a product of the Force itself (though I guess there's still conjecture about Anakin in that regard too -- which hopefully will be cleared up). What I think sucks though is that, as a storytelling mechanism they haven't brought new prophecies/legends into the storyline to convey. By that, I mean they could have had Luke discover some other prophecy, or as I mention below more info about the Chosen One prophecy. Perhaps not bringing that in is move by Lucasfilm to avoid the complaints there were about the prequels having them (though yeah.. abiding by fan's desires is another ****show of a topic itself). But by not having it brought up, or even teased, in either VII or VIII, it weakens the overall narrative -- if indeed she is a product of the Force.
I know I'd been kinda assuming prior to TLJ coming out, that post ROTJ, Luke was going to kinda help unravel the true meaning of the prophecy, if it tied into other prophecies, etc, and perhaps would even have learned from it that he personally doesn't have to be the one to take action all the time (hence the not returning from Ach To and instead just learning/waiting)... that the force itself is able to will that to happen -- in this theory, that action of the Force being via Rey.
Regardless, I think Disney/Lucasfilm would be better served to close the door on this chapter and jump someplace else in the timeline for their cinematic efforts.