Running the new OS on INTEL hardware is going to be slower than running on APPLE SILICON. No way around it. Running emulation is just slower. Which is why I probably wont' upgrade my intel macbook to the new operating system. Not to mention the fact that my version of premiere (the last one that doesn't require a subscription) won't run on the new OS.
Exporting the "Stems" of a project with and without plugins active is a time honored way to archive projects. That way you have the original tracks and the plugin affected track as reference. Opening 10 year old projects is almost always a challenge on something like reaper or pro tools since any plugins must be present, etc. On logic it's a bit easier since so much stuff is built in and fewer plugins are needed. Still, just exporting the stems is often easier. I do keep a disk image of my old boot drives for such reasons. If I need to, I can boot from an old drive, and open an old file.
There will be a big transition period in the music/film/tv production world as it's so heavily mac based. It is impressive though that the macbook air can edit 4k footage without dropping frames.
It won't be like running 2 languages at once like I feard, things will be installed depending on the computer. I suspect rather than power/speed the problems will be related to "bugs".
The post gave a great example of the switch made from x86 to x64, pc guys will relate to this much better. Today (for example in reaper) any x86 plug-in will work but crashes are common.
3rd party developers will fix these as things progress, but with mac as usual backward compatibility will be the biggest of problems (even worse as this is not only os but chip related too). We might see people looking for old mac's 10 years in the future for opening an old project.
My advice is freezing every track in a mix when it will be archived. It's not a perfect solution but based on my experiences trying to open 10+ year old project it will work best.