Where can we track dvd sales?

Good question. I also asked the forum about pre order numbers- I don't know if those are even tracked.

I suspect DVD sales would be at least a week late if they are anything like game sales.

A fully comprehensive tracking of DVD sales is actually impossible because of how retailers buy in the DVDs. Something of a rough guide is to look at the top selling sales charts to give some reasonable idea of a popularity indicator.

http://www.officialcharts.com/charts/film-on-video-chart/

Why? 

20th Fox is still contemplative about the future film(s).