Is (or will) Ferrocene be open source?
... exclusive early access to Ferrocene releases ...
exclusive
This phrase look suspicious, as "open source" and "exclusive" typically does not mix well.
Will it be a special version of rustc with private bugfixes, like in ~"we have fixed 19 bugs in rustc that can lead to miscompilations in your missing-critical program, so you better pay us for better private rustc instead of using buggy upstream version"~?
Or will publicly available source code be exactly the same as in certified version of the compiler, with the difference only being the legal warranties?
Or will it follow something like grsecurity model, i.e. technically open source, but please do not distribute (lest lose the subscription).