Here's a project using actual VF display tubes as an amplifier: http://www.hpfriedrichs.com/radioroom/vfd/rr-vfd.htm If you look at the wiggly plate current curves he measured, there should be plenty of harmonic distortion for tube audio enthusiasts.
BTW, the VFD used on the first link happens to be Noritake, that is, the same brand associated with work for the NuTube project, and the inventors of the VFDs, so this might not me new for them at all.
And also, by the way, almost the only brand still manufacturing VFDs that are easy to find on the market (at least buying one by one).
I think it won't. Because it looks like there's even a magnet on the Korg's tube. They might be leveraged that same research, and listed it as a prior art or paid him as co-inventor.
The confusing bit for me, and realize I'm not a patent lawyer but have patented a few things, the referenced articles first publication was in 2008. I was told that in the US (but not in Europe) you have one year from public disclosure to file for a patent. (In Europe you give up your patent rights if you disclose first.) So to patent this you'd want to have filed in 2008. Here it is 10 years later. So why hasn't a patent issued? I've seen them take 3 - 5 years but 10 years seems like a stretch.
My 1970s HP oscilloscope contains several Nuvistors (https://en.wikipedia.org/wiki/Nuvistor), which are nearly as small. 17mm x 10mm dia.