As outlined in
https://github.com/scala-ide/ecosystem/wiki/Releasing-a-scala-ide-version

Section "layout details and conservation strategy"

We currently have a complete mirror of the root tree of our update site as the staging area of the ecosystem. But at a given time, we have only one meaning for the "_next_" version of Scala-IDE regardless of whether this "_next_" version is a stable release or a milestone, or a release candidate.

It would make more sense to have one single repository (as opposed to 2) per flavor of the tool chain (Scala, Eclipse) that would contain this "next" version. Thus, plugin maintainers would be able to point a continuous integration server to a single URL to monitor the build of their plugin.

The information gathered from a build breaking would then be "it's not compiling for the next Scala version". Right now, compilation on one hierarchy (stable or dev) doesn't guarantee the other one hasn't been updated. Compilation breaking in one hierarchy may also mean it has been cleaned up (e.g. because the other has been updated, or more simply because it's been release to the public tree).