People have been saying this for many decades, and they've been wrong ever since. (I ran across, at one point, someone mentioning in the 1960s or so that they were loathe to design a new programming language because how could it possibly compete with existing languages like assembler, FORTRAN, or Lisp?) There are constantly new niches opening up and new areas of growth that a programming language can grow up within. It's a big world out there. There's probably a language stumbling backwards into success right now in China neither you nor I have heard of.

As so often, Alan Perlis said it best: "In a 5 year period we get one superb programming language. Only we can't control when the 5 year period will begin."