If this continues, expands and remains, it will be a matter of time until CBP collects the DNA of some US citizens entering the country legally and yet being held for further screening with or without being placed into detention facilities. Even having prima facie evidence of US citizenship and identity and being free of criminal history/activity may not be a timely shield against such governmental collection of DNA.
Even if this were restricted to detention facilities, what constitutes a detention facility may not even be static over time.