(Audio/DSP) plugins are a tricky thing, it is not uncommon for some of them to have assembly or processor specific instructions to squeeze out as much performance as possible. Your 'budget' in this domain is limited to only a few milliseconds ...
Even if it's precompiled and not at runtime, we don't really know what the performance looks like, especially in hand rolled assembly where something that isn't a one-to-one cycle match could have obvious effects.
> The system prevents you from mixing arm64 code and x86_64 code in the same process. Rosetta translation applies to an entire process, including all code modules that the process loads dynamically.
Apple has pushed XPC architecture for plug-ins for several years and has announced that these plug-ins will work in Rosetta for a Native host app. Audio Units will work as well.
The question is if those plugins are modules (shared objects/dynamic libraries), or if they are used via some sort of IPC to an external process. (or even an XPC service)
Rosetta 2 cross-compiles Intel binaries to ARM. Why would VST/AU plug-in binaries be an exception?