Food for thought: Not every BNB is possible with the 6 second limit, especially if you don't immediately hit them with it as they are getting up from Soul Steal. Don't do restands where you will just immediately morph back and get minus frames, be prepared to end for damage instead of restand. It's also worth noting that most setup specials disappear after Shang morphs back.
You also really want to get good at pressuring from the Soul Steal knockdown, knowing what you can do at different ranges so that you can capitalize on that great offensive situation for Shang. And you want to have a solid neutral plan ready, remember that you will win traditional projectile trades because you have the 20% buff. Right after Soul Steal, your risk is the lowest and the reward is the highest, and the opposite as your morph timer runs down. So risk/reward on mixups and neutral is constantly changing as you are morphed, and you'll want to play lamer and safer after you mix your initial few seconds where real combos are possible.