./pants changed and ./pants list-owners were converted away from being pants goals and toward being "root selection" options, and we should likely do the same for dependees.

So:

# rather than...
./pants dependees --transitive $target
# ...you'd run something like
./pants --dependees=transitive list $target

There are a few reasons for this:

1. it's more flexible, because you could use it with other goals: ie: ./pants --dependees=direct test $target.
2. there is a possible alignment-with/replacement-for the --changed-include-dependees flag, which represents a parallel implementation of the concept in TargetRootsCalculator
3. it would be cacheable in pantsd sooner than if we ported ./pants dependees into a --v2 task (as in this sketch)

One open question though is whether the --dependees option would include/exclude the original roots. That might also affect naming: if modeled after --changed-include-dependees, it might be a ternary option:

--changed-include-dependees=<str> (one of: [none, direct, transitive] default: 'none')