GCC-RS will never have the same level of investment as rustc, which means that either it'll rot or the entire ecosystem will rot due being tied down waiting for it to catch up.
Also, the Rust community at large is not at all enthusiastic about handing the language over to ISO. The design-by-comitee-based, incrementalist, waterfall throw-it-over-the-wall-every-3-years approach is pretty much the exact opposite of the continuous delivery-based way Rust is developed, and arguably one of the main reasons why C++ sucks.
Also, the Rust community at large is not at all enthusiastic about handing the language over to ISO. The design-by-comitee-based, incrementalist, waterfall throw-it-over-the-wall-every-3-years approach is pretty much the exact opposite of the continuous delivery-based way Rust is developed, and arguably one of the main reasons why C++ sucks.