The problem with Eclipse 4.x was that it had significant API changes/inconsistencies during the development of Eclipse 4.0 and 4.1. This made us think twice before supporting it at that early stage.
When the stable build of Eclipse 4.2 (Juno) was finally released in June 2012, Oxygen v14.0 was already very close to its own release date and it was simply not possible for us to tweak it in time to officially support the new version of Eclipse. Note that I said "officially", this means it still works, but there are issues (some significant).
However, since the release of Oxygen 14.0 we have dedicated plenty of development time to supporting Eclipse 4.2 (Juno) and I'm glad to say that it will be officially supported starting with Oxygen 14.1 (to be released soon).