Don't expect much
Tekken producer Katsuhiro Harada recently had a chance to clarify the Akuma and Tekken 7 crossover, noting that he was the only planned Street Fighter character at this time that would make an appearance. Harada says that he has "always been against" guest characters, but since Akuma "fits the bill," he could easily be tied into the story.
With the demonic pull and tint of the Mishima family, I definitely agree that Akuma and his Dark Hado backstory are easily entwined. Harada teases that they are open to more crossovers in the future (also known as money), but for now, this is it.
Tekken 7 Interview – Talking Console Launch, New Features and Unreal Engine 4 [PlayStation Lifestyle]