Personally, I am kind of indifferent - I think there are valid reasons for both distances.
*One course would be nice as far as meet management.
*Training-wise, the most significant thing is not equivalent race DISTANCE, it is equivalent race TIME. 4k/5k make it so boys and girls are basically racing the same amount of time. This, in my opinion, is the best reason to retain 4k.
*I agree that CC should be DISTANCE running, and the difference between track and CC is not as significant as maybe it should be. I think this is the best reason to go to 5k.
Personally, I think the absolute worst reason to go to 5k is the idea that "colleges want 5k times." In my opinion - who cares? Not my job. I can't believe there are good college coaches who cannot figure out who the good HS runners are based on 4k times and doing some research. Also, it is not the job of HS sports to structure themselves around a handful of elite individuals who a handful of elite colleges may want to recruit. HS is about participation and experience of being on teams, getting in shape and focusing on qualities that can help you elsewhere. So, I really hate the "college argument." Plus, girls going from 4k to 6k is already much less of a leap than boys going from 5k to 8 or 10K. It is already not much of an adjustment compared to guys.
I think the worst reason to keep it 4K is that "girls won't come out." That was the same argument for staying 2 miles instead of going to 4k . . . . . the facts just don't back it up - participation is great for girls CC overall I think. So, I don't know that it would matter much going 4k to 5k in regard to participation. I suppose though, it is still a potential concern. You would not want to decrease participation for the sake of racing further.
Be interesting to see where it goes - like I said, kind of indifferent myself. I am good with 4k. Could adapt to 5k as well.