No, current programs are not "written in x86-64". They're written in Objective C, C++, Swift etc. - which don't depend on the processor architecture - and
compiled to x86 code. Huge swathes of applications will simply require the developers to tick the "ARM64" box in XCode, re-compile and test: in many cases it will be far
less work than the recent switch to 64 bits, or the annual update to cope with the latest OS X version - which
could involve changing code or even re-designing apps to work with new security features.
Yes - there
will be exceptions where processor-specific code has been used for speed or optimisation, but in 2020 that sort of thing is overdue for replacing with calls to OS frameworks (Metal, Accelerate etc.) anyway, and other optimisation is best left to the compiler. Even then, we're talking about replacing
small sections of code, not a complete re-write of the app. Lovingly hand-crafted machine code is
hard work and no developer with any sense uses it unless there is a very, very good reason.
I'm not saying it's a non-problem, but its
nothing like the complexity of (say) making a Mac version of a Windows app or even a iOS version of a Mac app. Even with Photoshop for iPad, a huge part of the difficulty is totally re-inventing the UI for touchscreen, dealing with the limited RAM/storage of the iPad and the peculiar security restrictions of iOS.
The unavoidable problem areas are likely to be:
- Goodbye to x86 Bootcamp/x86 virtualisation/x86 Docker (but hello to iOS/ARM and ARM Linux/Docker and maybe ARM Windows)
- Any "abandonware" no longer being actively developed/supported (that hasn't already been killed off by Catalina and the loss of 32-bit support)
- Some big dinosaurs with loads of legacy code and huge ecosystems of third-party plugins
- Some custom hardware drivers - but that's only because certain manufacturers suck at long-term support, and they're just as likely to drop support for the next x86 version of MacOS anyway.
...most of which aren't going to be a big deal on a 12" MacBook replacement. The key would be how well Apple manage any transition on the more powerful machines. They
could of course stuff things up by trying to lock down MacOS or otherwise making MacOS for ARM half-baked, or pushing the transition of Pro machines too quickly...