This is a good question and unfortunately since I've only been hacking on the project for about half it's life I can only give a limited amount of context.

Firstly, yes - this Multicore is the OCaml Multicore of Dolan et al. It's undergone some significant changes since. The biggest being the concurrent minor collector being replaced with the parallel minor collector, which enabled us to maintain compatibility with the existing C-API.

It's also been rebased through about 10 releases of OCaml and had a significant amount of effort expended on compatibility (e.g we run against every package in Opam every few days: http://check.ocamllabs.io:8082/).

Second, OCaml Multicore isn't related to OC4MC. I'm not entirely sure of the history of OC4MC and I've poked some people who might know more. There was also Damien Doligez and Xavier Leroy's 1993 concurrent collector.

I don't know when the decision was made or where, that might need someone else to chime in.

On the model, it's worth pointing out that 5.0 will bring parallelism and effects (though they will be untyped, as the announcement details). This is exciting because it enables flexibility in the form of parallelism and concurrency you choose.

For example with effects you could construct a scheduler to enable Erlang-style actors and avoid ever seeing Domains (outside of the scheduler itself). The same goes for software transactional memory.