I actually have had a theory that Bandai Namco might choose Jin over Heihachi. We know Heihachi dies in Tekken 7, and we know in Tekken 8 Jin will be the main focus. We have seen Bandai Namco push Jin as the face of Tekken before in Tekken 3. So what if they use Jin in Smash Bros Ultimate to really solidify the fact he is now the main face of Tekken not Heihachi. Aslo Heihachi has been consistently chosen before in other cross promotions, but now that Bandai Namco is pushing Jin. They might say its time for Jin to be the one pushed. Im not saying it will happen, but it is a very big possibility. In my opinion its now Jin vs Lloyd in competition for the Bandai Nacmo spot. It could still be Lloyd, but I wouldn't dismiss that Jin might be in the running now.
Also how great would this be? Just my opinion, but Ryu vs Jin in Smash would be epic.