Ro Laren would have been wonderful in Kira's place, but the show would have of course evolved in a different direction than the canon story we know and love.
I would have liked to see a continuation of Ensign Sito's character like they had originally planned. She was such a wonderful character that was just beginning to redeem herself, only to die prematurely.
DS9 would have been a completely different show if Ro was the first officer and not Kira. That being the case, I wish that Ro had guest starred in at least one episode so that people knew what happened to her.
Also, I definitely think it is a shame that we never saw Sito Jaxa in a DS9 episode. In my book, she didn't die in that "shuttlecraft attack!"