The release notes (not really the "vision") are here:
It needs a few updates.
The vision is simply Groovy 3 back-ported to JDK7 minus the bits that don't backport easily (so explicitly no retro lambdas or anything like that).
It's just to help make life better and ease porting for anyone still stuck on JDK7. We don't have the resources though to keep maintaining
that branch, so the idea is to get it out and then let it be maintained by interested contributors.
So, the Parrot parser is there but not enabled by default.
Currently I think the main things we haven't tried to bring back is the current native lambda implementation
and I think perhaps one of the new caching classes.