Great sign of the continuing hard work and thought going into interblockchain communication in particular. As a BP candidate this has been one of our biggest open questions in terms of how best to prepare for it.
Development of EOSIO Dawn 4.0 code is ongoing in the ‘slim’ branch on github. We will be polishing it up and officially releasing it May 11, 2018. At that time we will move slim to master and tag a release. Developers who want to remain on the cutting edge can follow our progress on the slim branch.