Maybe? I don't know. I imagine we don't have any good ways to observe gravitational waves, even fairly strong ones with periods of millenia or even centuries which are still very short times on a galactic scale.

And apart from that, I think that we can only look at CMB and conclude that it's a bit wobbly. Must be quantum fluctuations, sure, why not, but is it only the quantum fluctuations? Or maybe the spacetime between us and CMB source is a bit wobbly too?

Another thing is large scale structure of our universe. Visualizations look like foam. Planty of chaos that wobblines can safely compose into.

I think the work of those scientists is very important because it might allowed us to pinpoint how strong distortions of the spacetime would need to be to explain what we see and maybe we could narrow down the range of frequencies which might gives us ideas how to look for them.

Simplistic and grandiose assumptions make our current best model of the universe a bit restrictive. To the point that we are starting to find direct counterexamples for our theories derived from it. Mature galaxies way too old. Megastructures way too large. CMB fluctuation not exactly fitting best theoretical models. Unreconcilable differences between Hubble constant measured from CMB and that measured from galaxies.

I think accepting a bit of chaos beyond what we currently believe is an inevitable way out.