Unfortunately IED (Soon to be renamed "NOM") doesn't support Git dependencies :(
I'm considering switching to npm2nix and Nix for my projects, because I got burned by NPM far too often. Also Nix can be used for all software, not only NPM stuff. With NixOS it also ties a nice "package", haha
Complexity isn't much of a concern since all dependencies should (ideally) me automatically managed by NPM.
The greater benefit is reduced duplication and reducing excessive folder nesting. The former saves space and the time required to download dependencies, the latter solves some serious issues with using NPM on windows.