Firstly, I'm not saying Kielwood is the holy grail, but the logic of thinking that a company that mainly focuses on profit will jump on a significally more expensive product in terms raw material cost is flawed. So I would discount that logic. I did ask Kazunori Miki personally when he visited me back in 2021 if Mezz would consider Kielwood and he was very quick to say no.
Personally I have made several Kielwood shafts and there's upsides and downsides. They are brittle, so cutting threads for the tennon needs a really sharp single pitch threadmill and threading the shafts for any big pin is best done by gluing in an insert of a less brittle material. The upsides is the harder surface and that you can turn the shafts quicker from dowel or square to a final diameter than you can with a maple shaft.