How is this different from debugging info? They should just use DWARF instead of reinventing the wheel.
As I understand in the not too distant future, everyone that absolutely despises Javascript and the whole ecosystem it re-invented will be able to merrily go about their way using the old familiar tools and languages from yore when they can compile to wasm.
Considering this wouldn't make much of a dent in the work needed to get tools like gdb/lldb to work with WebAssembly engines I don't think it's likely to be the best path forward for WASM.
As it stands sourcemaps are pretty much useless for a wide range of issues that we have with them and attempts to fix them went nowhere.
It's not a waste if you can leverage what your teams existing knowledge instead of learning the quirks and tricks of make.
It's not a waste if you can use your existing tooling (editor plugins, debuggers, unit test frameworks...) to process your build files.
I don't see how your argument holds ground. If everyone used make, tooling would support it, and you wouldn't need to learn the "quirks and tricks" of a dozen other systems.
The problem with make is that it's not portable, since it needs to call system specific binaries, like rm(1) vs del. There's also the BSD vs GNU divide.
Other than that, a newfangled tool like gulp doesn't even have a clean one liner for copying one file to a different location with a different name. It's absurd.
??
gulp.src("srcfile")
.pipe(rename("destfile"))
.pipe(gulp.dest("destloc"));
Compare to: cp srcfile destloc/destfile
Edit: In addition, the above gulp command reports success even if the file doesn't exist. If you want to check that, you need to import another library and expand the command with another pipe.