alt Hacker NewsIt is intentional to avoid non-free projects from building on top of gcc components.
I am not familiar enough with gcc to know how it impacts out-of-tree free projects or internal development.
The decision was taken a long time ago, it may be worth revisiting it.
Over the years several frontends for languages that used to be out-of-tree for years have been integrated. So both working in-tree & outside are definitely possible.