No one knows the reason why they changed their mind on female Viera hair, it hasn't been stated. I could speculate that it was because they want to treat female Viera/male Hrothgar as one race so everything needs to be a 1 to 1 ration. Modders who mod other races' hair on Viera an attest to how Viera ears are not a problem for any female hair that exists on other races except unique ones for Miqo'te. Viera ears are similar to Au ra horns, they're unique, they're not one piece like male Hrothgar face + hair is.

As for the chances of male Viera getting added? I see them as near 0. Yoshida himself never talks about Viera in a positive light, that tends to influence his decisions, which is fine it's his game. The only issue I have is with them not saying they won't be able to add the missing genders in the next few expansions, that I would respect more than saying "if we find a way to add them we'll add them." That's more honorable than leaving people hanging for 2 years.