I am sorry that this week I won't be able to really participate in this
thread, but I couldn't help mentioning that you guys are reinventing the
Self scheduler and so might want to take a look at that.

It includes a single primitive called TWAINS (transfer and wait for an
interrupt or signal) for switching from one process to another. When
Self starts up, it runs a single thread. At some point the scheduler is
started - it is a process just like any other. The only thing special
about the scheduler is that it calls the TWAINS primitives and none of
the others ever do so. There is no protection against this, however.

-- Jecel
P.S.: the scheduler difference was what made a friend of mine drop
Squeak and use Self for his PhD project several years ago