O'Brien and Kim: The Weirdest Shared Story in Star Trek

One oddality shared by Chief O'Brien and Harry Kim is what?

Version of themselves from another timeline replaced Chief O'Brien and Harry Kim! Prime O'Brien sends his future self back to save the station before O'Brien is exposed to radiation allowing him to leap through time and in the process dies. A hull rupture causes Harry Kim to be sucked into space and the ship to get replicated on Voyager. Janeway sends her Harry Kim to the original Voyager after self-destroying the twin ship. Thus, from the future, both characters were basically replaced by themselves!

Why did the authors kill O'Brien and substitute his future self?

As it happens, killing O'Brien was the closest they could have done to realize a dream from The Next Generation. Though they intended TNG movies, the authors wanted to kill Riker and replace him with his transporter clone, it was vetoed. Though it was only for an episode, the writers decided to go ahead and kill O'Brien; they were not dealing with the consequences of a brand-new character.

Why did the writers labor over substituting their future selves for O'Brien and Kim?

Actually, this was a quite handy approach to add a fresh character without having to deal with bringing a whole new person to the program. They merely had a few more memories from the future; they already had all the same experiences and connections since versions of themselves replaced them.

Has DS9 suffered any long-lasting consequences by eliminating O'Brien and substituting his future self?

For O'Brien personally, who experienced a rather existential crisis, the whole affair was really perplexing. Over time, though, it had not particularly altered anything on DS9. O'Brien's future self essentially behaved like Prime O'Brien, so the show was not substantially affected.

Why did the writers first substitute his future self for Harry Kim?

The authors aimed to generate a somewhat "what if" situation. They were curious about what would happen to the crew should the two Voyagers clash. Harry Kim was ultimately killed, but they transported his future self back to the original Voyager to ensure they lost a significant character and to have some lighthearted fun with the chronology.

This all means for the Star Trek series?

The writers aim to avoid totally alienating the public, yet they are ready to take some chances and challenge things. Keeping things interesting without drastically altering the program was by substituting future versions of characters. For the characters specifically, it also produced some excellent dramatic moments.