It was my first time seeing this concept art a few days back, and I must say that this makes much more sense.
Since King Arthur was supposed to be male, this Saber fits the role better in that regard. What would his personality have been like? I could easily imagine him having a Shirou/Archer-type disposition, or maybe he would have been similar to the female Saber.
As for the female protagonist, Ayaka would have been an interesting choice instead of Shirou. Quite possibly less whiny and wearing glasses is always a plus.
It seems like the only reason they swapped the genders around and changed the characters was to make the Fate story into an eroge.
Nasu (writer of the Fate storyline) stated:
“Even though sometimes he [Takeuchi] says impossible things, at the time the concept seemed simply ridiculous. Turning Saber into a girl, that’d completely destroy Fate! At first I was very against the idea, but after a while, I thought some of the difficulties that might arise could be resolved.”
It’s a pity Type-moon hasn’t made an alternate version of Fate/stay night using the initial concept characters.
Source: Type-Moon Wiki