Since the two are incompatible in a number of ways and RESTCONF forms our primary northbound interface, we are carrying them as two separate implementations.
While the RFC8040 implementation has taken some time to fully mature, it is now considered the preferred way of talking to an OpenDaylight instance. It is available as odl-restconf-nb-rfc8040 feature and installed as default.
The old implementation, as available in odl-restconf-nb-bierman02 feature, is considered deprecated, frozen and no longer maintained.
It is now time to drive the transition to RFC8040 home by migrating leftover documentation, CSIT bits and finally removal of the implementation.