The article is wrong about how conventional aircraft jet engines work. 80% or more of the thrust comes from a fan blowing air backwards. The jet engine simply drives that fan.
Turbofans do not operate in the same airspace as turbojets— not for speed, nor for altitude.
For those curious, the technical paper is here:
http://iopscience.iop.org/article/10.1088/1742-6596/825/1/012005/pdf