Also, I know you are interested in parallel variants of ASDF. It seems like this would conflict with the desire to enforce deterministic orderings, since if you have A must be before B, C, and D, but B, C, and D are unordered in the system definition, determinism would lead you to want to have a deterministic algorithm for ordering B, C, and D, but parallelism would suggest you separately compile B, C, and D in different images (each of which would have A loaded).
while we are at it, i would welcome a change/feature where anything unspecified would be randomly ordered.
so that issues come up while developing, not when the live system has a different filesystem order and boom, things just don't build...