In a nutshell. Imagine if the pioneer of F1 was the CEO the FIA and he just quits the FIA altogether due to conspiracy and other behind close doors drama. That's basically whats going on here. The founder and basically the guy who started it all leaves the main foundation of drifting (D1GP) because of apparent injustice in it's ranks and it's hidden ties with the Japanese underworld (yakuza and as well as supposedly some teams being funded secretly by them. Its just a whole mess of things at the moment. Sure D1GP will porobably go on for another year, but it'll dwindle for sure.
Most likely we'll see a new series in the future by both Inada and Tsuchiya, thats more fair and favors less of million horsepower machines and multicar powerhouse teams and less favoritism judging.