[bonzini]

Currently the SI is making the triple point of water fixed. I think his point is to make the Boltzmann constant fixed, like the SI is doing for the speed of light, and derive the Kelvin from there. For example 1K could be the temperature at which an atom of (insert some gas here) has a mean kinetic energy of 1.3806488 * 3/2 * 10^-23 J.

However, you have to make sure the definition can be made into an experiment, unlike the old Ampere definition from the article. A definition that mentions perfect gases wouldn't work, if no actual gas exists that can provide a better precision than the triple-point experiment.

Edit: the Kelvin is changing too: https://www.eurekalert.org/pub_releases/2017-04/pb-rft040517...