Think hard before adding new feature. Think of a damage it could cause used improperly. Think of cognitive complexity it introduces. Only add a feature generic enough to cover lots of useful cases instead of just some corner cases. Let's better have a list of recipes for the latter.
Do not introduce unjustified complexity. User should not be forced to learn a whole new programming language to work with a tool. Instead, the tool is based on limited set of simple concepts, like goals + dependencies + handful of directives + familiar shell language (bash/sh).