Short answers, pulled from the story.
Katsuhiro Harada announced Tekken X Street Fighter on the 24th of July 2010 at the San Diego Comic-Con. The project was revealed as a crossover title merging the 3D universe of Tekken with the 2D world of Street Fighter.
Katsuhiro Harada officially announced that development on Tekken X Street Fighter was on hold in April 2016 to avoid splitting the communities behind both franchises. The decision prioritized the long-term health of both franchises over the immediate release of a game that might have alienated one side of the fanbase.
Katsuhiro Harada stated that the game was approximately 30% complete when production was halted in 2018. The project had been in the works for six years and had already seen significant investment from both Namco and Capcom before the decision to pause development.
Some of the animations created for the cancelled Tekken X Street Fighter were reused for Akuma in Tekken 7: Fated Retribution. This connection was confirmed in June 2021 during a broadcast of Harada's YouTube show Harada's Bar Radio.
The cancellation of Tekken X Street Fighter was confirmed in June 2021 during a broadcast of Harada's YouTube show Harada's Bar Radio. Harada stated that the game had been cancelled and that some of the animations created for the project had been reused for Akuma in Tekken 7.