Interesting response, and since it is coming from someone I regard very highly in the MorphOS Dev. Team, I don't need to dig any deeper into figuring out what AxRuntime is and how exactly it works.
The description of it running on multiple cores, and having protected memory usage, seemed like a "Good Thing" to have,
But MOS devs don't use and know AROS (hosted). If you run one AROS instance (runtime) per (big) app things like isolated address space/memory protection (between app A running in AROS instance/runtime #1 and app B running in AROS instance/runtime #2)/resource tracking/multiple core use come automatically and for free.
Now for allowing ~ SMP (multiple core tasks/processes) *inside* each AROS instance/runtime which I'm skeptical about too, it's surely possible to have that a runtime option so it can be decided per-app (runtime) whether to activate this or not, as most apps would not take big advantage of it (and system tasks like Intuition/input.device hardly need any cpu resource).
Here is an old video of more than 20 AROS instances (~runtimes) running at the same time. Each Amiga-looking window/app is from a different instance. All 4 cpu cores of the machine used.
The desktop/icons in the backround is Linux stuff, also there's some Linux terminal windows intermixed.