> Maybe I'm missing something, but don't the vast majority of applications don't care about what architecture they run on?

There can be issues with moving to AArch64, for instance your Python code may depend on Python 'wheels' which in turn depend on C libraries that don't play nice with AArch64. I once encountered an issue like this, although I've now forgotten the details.

If your software is pure Java I'd say the odds are pretty good that things will 'just work', but you'd still want to do testing.

Sure, but you're talking about short term problems. RPi, Graviton, Apple Silicon, etc... are making AArch64 a required mainstream target.

That's true. AArch64 is already perfectly usable, and what issues there are will be ironed out in good time.

Even if the applications don't care, there's still the (Docker) container, which cares very much, and which seems to be the vehicle of choice to package and deliver many cloud-based applications today. Being able to actually run the exact same containers on your dev machine which are going to be running on the servers later is definitely a big plus.

Docker has had multiarch support for a while and most of the containers I’ve looked at support both. That’s not to say this won’t be a concern but it’s at the level of “check a box in CI” to solve and between Apple and Amazon there’ll be quite a few users doing that.

Our experience as well. We run a stack that comprises Python, Javascript via Node, Common Lisp and Ruby/Rails. It's been completely transparent to the application code itself.