This is a change that I made to wikimedia's fork which we found quite useful. It's a trivial change but upstream wasn't interested. It could be made configurable with the default set to enforce milestone ordering or the ordering enforcement can be removed entirely, as I did for Wikimedia.
Some rationale for the change:
- Patch: rPHAB042685bdf637: Allow milestone columns to be reordered.
- epriestley was very much against this idea but wikimedia's users loved it.
- Milestones, unlike subprojects, are mutually exclusive, so a task can only be in one milestone in the superproject. This has the convenience that adding a task to a milestone automatically removes it from any sibling milestone within the same superproject.
- Reordering milestones is convenient when you want to treat milestones as workflow steps rather than sequential numerical versions. Example: https://phabricator.wikimedia.org/project/board/20/
- upstream product vision was to use milestones exclusively for sequential things like "Maniphest V2" or sprints.
- Wikimedia chose to abuse milestones for workflow steps and being stuck with the ordering that phabricator enforces was a big inconvenience for that use-case.