It may not be an acronym but it is literally a variant of John Darcy (the hero from one of my favourite books Pride and Prejudice). “Jack” is actually a derivative of John. And Dorsey originated from the Norman “De Orsay” the same as Darcy. So “Jack Dorsey” is just a more Irish way of saying “John Darcy”. Lol I know weird, but I kind of love it.