Sorry, I'd always thought it was common knowledge that Kira was originally intended to be Ro. I guess not everyone's as obsessive as some of us! Most of the concept of DS9 was built out of the Bajoran-Cardassian situation as described in the TNG episode "Ensign Ro" so it was a natural fit to spin off the popular character from that episode into her own show.
But I agree that Kira turned out to be better. Aside from Nana Visitor being an excellent actress who we wouldn't have seen otherwise, Kira's character could more easily stand for the Bajoran side of the equation against the Starfleet commander, which Ro - as an actual member of Starfleet, however troubled - couldn't have done.
As for the Ro-on-Voyager rumour, I have heard it but I don't place as much stock in it as the confirmed Ro-on-DS9 information. She does have certain character traits in common with Chakotay (or at least with the character Chakotay was supposed to be if not what he actually became), but IntrepidMan is also correct that she would have been very similar to Torres. I don't think she could have replaced Torres because Ro never had anything to do with engineering IIRC - she was always tactical. And if she had been there as first officer, it would have led to Voyager being a very female-dominated series, as four of the most prominent characters - Captain, XO, engineer and "alien-perspective character" - would have been women. Not saying there's anything wrong with that, it would have made for an interesting dynamic, but it certainly hadn't been seen before on Star Trek.
FYI, in TNG "Preemptive Strike," when Ro refers to a trainer at her advanced tactical course who quit and defected to the Maquis, the intention was that she was referring to Chakotay.
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