Also possible with MQTT v2. See Marketplace MQTT Event Bus. If you are using JSR223, there is a library module you can use, MQTT Eventbus by rkoshak · Pull Request #257 · openhab-scripters/openhab-helper-libraries · GitHub.
There shouldn’t be any missing bindings. To my knowledge all current OH 1.x bindings will run on OH 2.
It is possible to mix and match the MQTT 1 event bus on your OH 1 and the above approach on your OH 2 instance.
IIRC, the OH 1 REST API may not be sufficient to provide a good federation between the two instances. But if it is, I suspect the effort to get it set up and working would be more than using MQTT.
NOTE: I federate two OH instances, one of which is 100 miles away.