I really want to like this and conceptually the idea of being a simple command is appealing. That said, I feel like writing a shell script and especially their

I really want to like this and conceptually the idea of being a simple command is appealing. That said, I feel like writing a shell script and especially their example is really really off putting. For one the flexibility it offers means people are going to use that flexibility to do weird stuff, second a shell script far too easily captures dependencies to it's environment again making things non-reproducible. If you allow people to put local paths, dependencies on local weirdnesses and so on in their build scripts they will, I've seen it happen time and again.