I don't expect it to be too painful. Most common software has already been build for ARM on Linux. A lot of things have event been built for Apple's ARM chips r

I don't expect it to be too painful. Most common software has already been build for ARM on Linux. A lot of things have event been built for Apple's ARM chips running iOS, though the App Store restrictions have limited the usefulness of these builds. Unmaintained closed source software will stop working but most of these applications were already killed by the removal of 32-bit x86 support in Catalina. The biggest potential issue will be how people get hardware for doing the builds. Hopefully Apple will provide a good way of cross-compiling or a new machine that is suitable for datacenter deployment (ARM based mac mini?). We'll have to wait for the WWDC announcement to find out.