For it to become a thing we would have to redefine our temperature scale to have more numbers below zero.

What would have to happen? Advances in quantum physics that cause us to adjust our temperature scales. Quantum states do allow for temperatures below the floors for K/C/F scales. But quantum conditions don’t extend to the majority of matter that we observe as our physical universe.

So it’s possible to go lower than the floors of our temp scales very specific, extreme, and limited circumstances* that don’t apply to the whole of our physical universe; therefore, from a practical perspective, they don’t matter when measuring temperature of the physical systems we know.

*As far as we’re now aware, and can measure. This may change as we learn more.