Now that the individual package's gemspec is serialized into it's directory, Nu is in a good position to do this. It can find each of the projects that are at the tops of the dependency graphs and, with each of them:
1) ask gem to update to the latest version
2) remove all dependencies (owned only by that project)
3) `nu install` the project again

We should probably keep track, for each top-most project, if a specific version was requested with the –version flag. If so, it would be opted-out of the `nu update` command.