I think that Rory is closer to a title shot than Khabib. Also, if Rory beats Ellenberger in any way other than a close decision then he will have a good chance to beat anyone in the division except GSP, who I think would beat Rory as they currently are. Of course, GSP is exactly the problem, isn't he? Rory and GSP have continued to insist that they won't fight each other, but Rory has said that they have an arrangement, although no details have been given.
As long as GSP is the WW champ Rory won't take the opportunity to fight for the title. Thus the question we need to ask is, "how can GSP no longer be WW champ, and how likely are these?"
First up, Hendricks has the next shot at SP. I think Hendricks only has the first round to land that power shot and finish GSP, after which his KO power diminishes, along with his chances of victory. He most certainly could land that shot and (T)KO GSP, but GSP's speed, distance, management, and defence are just so good that it will be hard for Hendricks to do so.
The next biggest threat to GSP is probably Ellenberger because he has very heavy hands and great TDD, similarly to Hendricks. Unfortunately, if Rory beats Ellenberger then he will not only be set further back from a title shot, but if he can't beat Rory then he probably can't beat GSP either, and if Rory loses to Ellenberger then Rory will be set further back from a title shot, in which case it will be a while until he can work his way up again.
Condit is the only other guy who I see as a threat to GSP, especially if he improves his TDD. Other than that, I don't think anyone else has much of a chance of beating GSP unless we see big improvement from them.
So if GSP is unlikely to lose the belt, the only other options are retirement or moving weight divisions. He's been pretty unenthusiastic about moving up to MW, to put it lightly, though he has mentioned that moving down to LW would be easier, which I can understand given his body type and how difficult he has said it is to keep the amount of muscle he has. It is very possible that he might just retire once Rory has gotten very good and shown that he can hold onto the title for an extended period, but GSP has also said that theirs still more he wants to do in MMA.
In conclusion, while Rory may be very close to a title shot, I don't think he'll actually take the opportunity any time soon because I don't think GSP will lose or vacate the belt in the near future.
In Khabib's case, he's definitely a very good prospect and has already defeated some good competition, but he hasn't been as impressive as Rory. While he is certainly a future top contender, I don't think I've quite seen what I would need to in order to say he'll be a champion in the next couple years.
I would say that he need at least 2 more wins to get a title shot. Given that LW is such a competitive division, and that he hasn't yet shown me that he's already dominant force, that is no easy task. Even if he does, his chances of winning are certainly not guaranteed.
At this point, I wouldn't make any predictions about who is more likely to win the title first. If GSP wasn't the WW champ then I would say Rory without hesitation, but GSP IS the WW champ and I don't think he'll lose any time soon. Khabib will certainly be a top LW in the future, and looks like he'll have a good chance to become champ, but he hasn't seemed impressive enough to warrant betting that he will be.