It is interesting to note BMW is likely to continue with the 'S' designation here for M motors despite saying they will not longer use it. The reasoning in this application is likely because the S58 is a revision of the already 'S' designated S55. If it was a revision of the B58 engine, you likely would not see the 'S' designation.
BMW is expected to increase the power to 450 horsepower but we all know the S55 motor already produces more than 450 horsepower. The reason for this increase will likely be to give the motor more torque to move heavier X SUV's which will also be sending power to all four wheels through an automatic. That means a less efficient drivetrain than the dual clutch and rear wheel drive F80 M3 and F82 M4 models.
It is possible BMW equips the new M SUV's with a dual clutch transmission but considering that they are going to an automatic for the upcoming all wheel drive M5 and that the X5 M and X6 M both utilize automatic gearboxes prepare to be disappointed.
Expect more details as we get closer to the 2019 model year launch.