As of October 2018, governance of the BigchainDB software began transitioning from BigchainDB GmbH to the IPDB Foundation. That includes defining the roadmap. If you'd like to be involved with that, then contact the IPDB Foundation.
At the time of writing, BigchainDB was at version 2.0.0 Beta N, where N was a number like 9. To see the latest release, go to the BigchainDB Server releases page on GitHub.
The only thing that must be done before the release of BigchainDB 2.0.0 (with no beta) is to update it to work with Tendermint 1.0.
Old files, including the old ROADMAP.md file, can be found in the archive folder.