Always interesting to see new ideas - and if it's QCTPs then it's QCTPs

I'm sure that that design is fine for a small lathe, but I don't think that it would scale up to a larger one with much larger cutting forces as the cunning slot will tend to open up as the expanding collar grips it.
It must be possible to make the vertical part of the locking shaft longer so that an unslotted holder will lift up clear of the central spigot, then tilt to allow the handle to pass through it.
Andrew