In 2010, Namco Bandai (now Bandai Namco) and Capcom announced a crossover between Street Fighter and Tekken, that would be made up of two games - one based on Street Fighter and produced by Capcom, the other based on Tekken and produced by Namco. In 2012 we got the first half of that crossover, with Street Fighter X Tekken, but since then, little to nothing has been said about the other part of the deal.
In a recent interview, Katsuhiro Harada confirmed the game is still coming, although he recognises the game was originally planned to be released "much earlier than we're currently looking at". Harada stated that Bandai Namco decided to delay the game due to a saturation of fighting games in the market, but he assures the game is still being worked on by around 40 members.
Harada mentioned that he wants Tekken X Street Fighter to surprise people when it is re-announced, but he could not commit to a launch within the next 2 years.