Singapore has had Global Entry-type procedures for a long time - their citizens and permanent residents just swipe their passports on a reader and walk right in.
Mr. Jeeves wrote: “...but as a US citizen in good standing it can be argued that you deserve the presumption of Global Entry rights and privileges rather than being forced to prove you qualify and then having to pay for them.”
So, how does a TSA employee know you are a citizen if you show up to board an aircraft?