The X3 M is expected to launch with the S58 and later on in the X4 M as well. The S58 is BMW's M motor based on the B58 and should have a power output around 470-475 horsepower.
http://www.bmwblog.com/2017/12/23/next-bmw-m3m3-x3mx4m-might-get-475-horsepower/
http://www.bmwblog.com/2017/12/23/next-bmw-m3m3-x3mx4m-might-get-475-horsepower/