As I remember it, what Navratilova was saying she wanted to do was play with Hingis as her partner,because then she feels she would have done everything of significance in doubles.
They have already faced each other across the net, both in singles and doubles. The singles match up was just an exhibition match in Italy when Hingis was about 12.
But they actually played a tour doubles match against each other, I think in 2001. Navratilova and Sanchez-Vacario played Hingis and Kournikova in a match in Germany, either at Filderstadt, Hamburg or Berlin, I don't remember which.
Martina and Anna won in straight sets.
But I would love to see the two Martinas playing as a team in a doubles match.
You would then, in my opinion, have the two greatest doubles players in history on the same side of the net.