Just to be complete:
What is not working currently is the compatibility between 1.6 and 2.0 for custom plugins. Especially code for Agent bakery, clustered checks and some SNMP checks is not compatible. Tribe29 is currently investigating a solution to allow installing code for 1.6 and 2.0 in parallel and only deploy the code which fits to the according version. In parallel I have an unofficial and not very well tested solution as plan B for this limitation.
regards
Michael