The fact is that nobody really knows of Toyota has plans to work on a Toyota Supra successor or not but most believe that they are working on one and that the question should be when it will be arriving.
Well, new reports are now suggesting that the new Toyota Supra successor might be looking at the Lexus GS and LS for its engine option. It this rumor is true, the Toyota Supra successor will come running on a twin-turbocharged V6 engine that will be delivering about 400hp and 300lb ft of torque.
Of course, other believe that instead of using one of their own, Toyota might end up using the engine from BMW. Their new partnership had lead people to believe that Toyota could be looking to use the BMW engine to power up their own model.
All of these are just speculations right now until BMW comes out and confirms them so take it all with a pinch of salt if you can.