According to an internal build of iOS 13, the R1 chip serves a similar function to the M-series coprocessor. It will use sensor data to figure out where the iPhone is located in 3D space.
The Rose coprocessor will add support for an inertial measurement unit (IMU), Bluetooth 5.1 features, ultra-wideband (UWB) and camera (including motion capture and optical tracking) sensor data to not only tell where the device is but also fuse this sensor data together to find lost Apple Tags and aid in the processing of People Occlusion from ARKit. Given the overlap in sensor data collection and processing the Rose coprocessor may replace the M-series motion coprocessor.
Currently, the M-series coprocessors only use data from the accelerometer, barometer, compass, gyroscope, and microphones.