Cond-expand is nice because it allows as many different implementations of Scheme as there are implementations of C (where we have #ifdef and Autoconf). On the other hand, though, it implies the same problems as we have with C. It's not very beginner-friendly (unless one sticks to one implementation) and makes portable programming hard, leading easily to "vendor lock-in". So the longer-term goal has to be to improve Scheme implementations (and possibly the standard) to reduce and minimize the use of cond-expand.