Couldn't certain areas of RISC OS be open-sourced, and others left in binary-only form? For example: if they can't get permission to distribute ShareFS source straight away, that doesn't stop it being available in assembled-module form. I'm sure that just starting to open RISC OS would create a productive tidal wave - any modules with lost or unavailable sourcecode could be replaced with other people's versions anyway. In some cases, it may help remove the "dross" - old legacy code that was in need of replacing anyway.
Congrats to Castle for making a very bold move. Chris' (unnamed) "well-placed contact" sounds like a glass-half-empty sort of person.