It seems to me that all build systems are just DAGs with syntactic sugar and functions. You could do away with build systems entirely if there were some Unix commands that manage an arbitrary DAG, where the state is kept out of band (in a file, in a database, etc) so you can operate on the DAG from any process. That way the shell (or any program, really) becomes your build system and you can compose any kind of logic…
Programs are just DAGS with syntactic sugar
0001 GOTO 0002
0002 GOTO 0001
How would that be a DAG?