Show current folder size in Nautilus

The reason this information is not in the statusbar is probably because it requires a lot of disk reading to find the disk usage of a directory. Consider opening /. It'll have to recursively traverse the entire filesystem in order to find the disk usage. The ammount of free space on the other hand, is very quick to retrieve since each filesystem keeps track of this.

Right click the folder in nautilus and select Properties. The Basic tab shows how many items and total size. Not on the bottom but the information is there.

It is not possible, and you would have to file a bug report requesting this feature.