Couldn't you run a VST host in the Rosetta environment for your x86 VSTs and run everything else native in ARM in a separate host? Or does the VST model require that all the VSTs loaded run synchronously within a single process?
There are ways to bridge it but basically you have a native plugin shim that talks to a process running the target arch and essentially passes protocol messages back and forth. Was common for a while on windows when many plugins were 32bit only and wouldn’t run in a 64 bit host
It's possible, but it would have to be a built-in feature of the DAW to be convenient, and could seriously compromise performance even if optimized.
Let's assume an ideal implementation where there is only one process per architecture. Take a 100 track project with two plug-ins per track (say, compressor and EQ). If the compressor is x86 and the EQ is ARM, that's 200 context switches per audio period. That makes it impossible to run at small buffer sizes. A very smart flowgraph implementation could attempt to batch everything into the minimum number of context switches, but that has other problems with threading. It's very hard to get this perfect.
This solution works fine for when you just have a few straggler plug-ins of the wrong architecture, but it would still require quite complex engineering by the DAW to make it work transparently to the user. Consider, for example, that the plug-in UI needs to embed in the DAW across a process boundary.
