No hazmat license is required to obtain thorium nitrate, though there are certain shipping restrictions. The secret seems to have been in the way Kodak layered it into the paper, so that the paper didn't need to be mordanted just before use like other options. Some of us have experimented with uranyl nitrate. There have been many variations of this process over its long history; and in its heyday, commercial versions of materials were made not only by Kodak, but by Color Corporation of America, the US Army, certain Hollywood interests (for still image prints from movie frames), and at least two other companies. I'm am experimenting with version of wash-off relief, which is easier to control than the later tanning process of matrix film, but takes a little longer to develop. But I suspect your last paragraph, falotico, is erroneous. The transfer step is fairly fussy, regardless, esp to pH variables. And letting a matice sit too long will result in a lot of dye bleeding. Dye Transfer could easily be revived if there were enough people interested in it. The biggest danger is the extinction of appropriate transparency or slide films themselves. And it's damn hard to work from acetate base, which are not dimensionally stable. Pan Matrix film is
a different subject. It is unlikely there will ever be a market demand for that again. I hope I can find enough time once I retire to work with
my supplies of Efke matrix film. So far, I've just practiced the chords and figured out the basics, including how to make very precise color
separations with current films. I already have plenty of 8x10 transparencies on hand to work with.