Short answers, pulled from the story.
Katsuhiro Harada stated in April 2016 that development was put on hold to avoid splitting the communities behind both franchises. At a 2018 livestream, Harada confirmed the game was about 30% complete when it stopped. In June 2021 it was widely understood to be cancelled, though Harada never used that word explicitly.
Tekken X Street Fighter was being developed by Bandai Namco and would use the 3D fighting engine of the Tekken franchise. Street Fighter X Tekken was produced by Capcom and used the 2D-style gameplay of Street Fighter IV. The two were announced on the same day at the 2010 San Diego Comic-Con as companion titles.
The game was announced on the 24th of July 2010 at the San Diego Comic-Con by Bandai Namco producer Katsuhiro Harada. No gameplay images or videos were shown at the time.
Harada stated the game was about 10% complete in April 2012. By the time development was put on hold in 2016, he said the team had reached approximately 30%, a figure he reiterated at a 2018 livestream and again in June 2021.
Harada revealed in June 2021 that some animations created for Tekken X Street Fighter were repurposed and used for Akuma's appearance as a guest character in Tekken 7: Fated Retribution.
Yes. Ono, who had left Capcom by then, made a surprise appearance on stage with Harada at EVO 2023 and said the two had left some homework behind. He began saying the title Tekken X Street Fighter before Harada chased him off stage.