In Flix, Datalog constraints are first-class values. This is strictly more powerful than a macro system. For example, the Datalog programs that are constructed can depend on input values to the program. This is not the case for macros which are expanded compile-time. (Unless you have some kind of reflection in mind...)

EDIT: I hope to explore a macro system for Flix in the future. So we are definitely on the same side of the issue; just wanted to point out that the current system is more powerful.