Is reversing the stem (pointing it backwards) a safe way to reduce reach length? Assuming a steerer/fork/brake/cable setup that does not rely on the stem facing forward: is it safe to point a stem backwards as a way to reduce seat-to-bar reach (i.e. as a way to 'fit' a too-large bike to a smaller/shorter person)? If not, why not?
No, it would not be particularly safe. The steering would get extremely twitchy and difficult to handle.