As for compatibility, Apple managed exceedingly well the moves from 68K to PPC and then to Intel, even keeping some binary compatibility. Few companies ever did that - DEC comes to mind, making VMS and Ultrix move from VAX to Alpha, and IBM moving the iSeries from AS/400 to POWER. iOS software will continue to be written for ARM for as long as we can see. macOS can, eventually, move to ARM too - if Microsoft can do it (emulate x86 at Celeron speeds on Snapdragon), Apple certainly can.
