For those saying that Miles and Kira would have been a better pair than Miles and Keiko because you didn't like Keiko or that the chemistry was better with the Chief and the Major: How do you justify that in the story line? A man leaving his family to be with his superior officer?
I think the only way to make it work without making O'Brien seem like a complete dog that abandoned his family (something that would have been way out of character for him) would have been to kill Keiko off.
Agreed it's a bad idea. DS9 was not supposed to be a soap opera anyway.