Sorry, but Square Register really cannot replace 99.999% of cash registers out there. The article is inaccurate in claiming that it can.
I'd happily bet that the Square team, and the evolution of the Square payment products, will.
I think of the square reader as the mailed dvd is to netflix. I suspect Square feels the same way. Their customers love them, they are disrupting a very non-innovative industry, and they've gotten customers fast enough, and sustained growth long enough, to have hit escape velocity.
(I don't work for Square, unfortunately; I did work for some NFC payment stuff in the past, and tried to launch an ecash system in the 1990s.)
Disclaimer: I'm biased, as I am behind FaceCash Register (https://www.facecash.com/register.html), but it means I also know what it took to build it.
Here's the only article I could find in a ~1 minute search that explains in more detail the concept: http://www.article13.com/A13_ContentList.asp?strAction=GetPu...