TFA seems to be wrong about this including US citizens. While I think fingerprinting anyone, citizen or not, coming into the country isn't something we should be doing, and certainly not when exiting, the bit about fingerprinting exiting US citizens is found nowhere other than in the article from IT News Australia. The actual DHS press release is very specific that this is a planned extension to US-VISIT and, as such, only applies to non-US-citizens:
Several additional articles all clearly indicating that this applies only to non-citizens:
Build a system that even a fool can use and only a fool will want to use it.