Back in the 20th century, the grimdark fantasy tradition had its beginnings in Michael Moorcock's Von Bek novels (The Warhound and the World's Pain, etc) which surely inspired Games Workshop's Warhammer RPG. In the early '90s, Jamie and I signed with GW to write a pseudo-Japanese supplement for Warhammer, which made sense given that the Sengoku period makes the Thirty Years' War look like a tussle between two drunks outside a kebab shop. But enough of me and Jamie...
Tetsubo had been commissioned by Paul Cockburn. Unfortunately he left GW the same week we delivered the manuscript. The new people in charge of roleplaying games there didn't have much enthusiasm for an Oriental take on the game -- and possibly not for roleplaying in general, as soon after that I think GW passed the Warhammer licence on elsewhere.
So that left Tetsubo in limbo -- or rather in Yomi -- until 2018, when Daniel Fox of Grim & Perilous Studios asked to adapt it as a supplement to his Warhammer heartbreaker, Zweihänder. The good news was the renewed spark of interest drove me to dig out the Tetsubo manuscript and scan it all, most of the book never having even been saved to disk and only existing in a faded dot-matrix-printed box of papers. The bad news: after a burst of activity it sank back into the land of mists, and after a year the contract lapsed.

But those are all just distractions. The bottom line is, a year on, Jamie and I could see that Tetsubo just wasn't going to happen. At least, it will only happen if we do it ourselves.
Currently we're mulling over whether this is worth doing as a Kickstarter. We'd need to rebuild it around a different game system, of course, and our first thought was Powered By The Apocalypse, which we enjoyed for its simplicity when we played our Sagas of the Icelanders campaign, but the appeal of Tetsubo will surely be to traditional roleplayers whereas PbtA would take it in a whole other narrativist direction. So not that.
One option is to use a variant of my Tirikelu RPG, but I'm not sure that would make best use of the skills and career paths in the Tetsubo book. I intend using Tirikelu for my Abraxas RPG (a good fit, hopefully, being science fantasy) and also Tirikelu isn't GURPS; we can't just tack it onto everything. Jamie suggested using a variant of my currently-in-development Jewelspider rules, on the principle that OSR players and Warhammer fans might have at least a nodding acquaintance with Dragon Warriors.
But then we had a brainwave. Paul Mason is an Anglo-Japanese academic who has lived in Japan for over twenty-five years. He's not only an authority on Japanese culture and history, he's also an editor, author and RPG designer with his own (as yet unpublished) game Outlaws, based on the stories of Liang Shan Po. What if we used the Outlaws system for Tetsubo? Not only would the gaming world get a taste of a brilliant and authentic Eastern-influenced RPG, but we'd get an extremely erudite Japanese scholar on board to consult on the final manuscript.
We asked Paul, he said yes, and that's the plan right now -- unless somebody throws an even better suggestion into the comments below.
Further reading, viewing and playing: