For a non-monorepo package you can simply point directly to the Github repo. This case is similar, but you want to scope it just to a single package within the repo. For those that make monorepos they don't necessarily need this feature. It's for those that use projects that use monorepos. Telling them to not organize their projects into monorepos doesn't help people who make use of these projects.

If npm installs a git repo, it assumes that the git repo is the package. I don't really know how we could specify a sub-path easily, since all parts of the git url are already used for other things.

This is more a rhetoric question as this seems to be quite hard ;-) There is a long discussion about installing a subfolder of a repository and monorepos in general at the NPM Github issues (yarn misses this feature, too). The thing is that this makes it quite hard to report issues of your project as one can't test the current master easily. Do you recommend a way how to use the latest Github version?

"neutrino-patch": "git+https://github.com/davidje13/neutrino-patch#semver:^1.0.1"