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 aimed to merge characters from both franchises into a single game with a three-dimensional gameplay engine.
Development officially stopped on Tekken X Street Fighter in April 2016 to avoid splitting the communities behind both franchises. Katsuhiro Harada stated that releasing the incomplete title made no sense from a business perspective by May 2019.
Some of the unfinished animations from Tekken X Street Fighter were reused for Akuma in Tekken 7: Fated Retribution. This repurposing allowed the team to salvage work done before the halt in 2016 during EVO 2023.
Fan voting results did not determine the final cast for Tekken X Street Fighter despite a poll launched on the 4th of March 2012. The data served as one research method alongside other internal decisions rather than directly driving the lineup.