We needed more Trek episodes where they found people from other timestreams and couldn't return them. We got Tom Riker but I think that was it. Stargate had a couple examples of this though one of them was androids.. but they kept them!!
Now this wouldn't work quite so well with Voyager because you'd have two of whoever on board but it would have been nice to see it happen on the other series, with the occasional storyline about other so and so. Even better if other so and so came from some crap hole timeline or from a much better timeline and thought this one was the crap hole.
OMG IMAGINE THAT! If someone AU actually thought this Roddenberry blessed timeline was a crap hole!