2.6/3.0-- has only undergone alpha releases. The fact that 2.7/2.8 are missing and that people stop to think is a good thing.
We are planning breaking changes for 3 (and hence 2.6/3.0--). With semantic versioning, 2.6/3.0-- should not have such changes.
So it really should be versions 3 and 4 but since we are going to drop support for 2.6/3.0-- straight away, it hardly seems worthy
of a dedicated whole version. I think 2.9 is a good compromise version number.
Dropping it altogether is another option but if you remember it was non-committer contributors that wanted this change and did
most of the (original at least) contributions. We've done all the work, I say let's just release as 2.9 and then drop it. If outside
contributors want to continue bug fixes on it, so be it.