I follow the commits in github with great interest.
I was just wondering what is the main “idea” behind the 6.0 release. Since it is a new major version with breaking changes I could imagine it is e.g. driven by cleanup historical code, or performance, or preparation for upcoming features etc.
Just curious 
I would checkout the release notes: https://github.com/bndtools/bnd/wiki/Changes-in-6.0.0.
There are dependency updates including base Eclipse, Maven, and Gradle supported versions.
The Bnd Gradle plugins have been rewritten in Java and have a number of minor backwards incompatible changes necessary to keep up with changes in Gradle itself.