The /active_tasks endpoint returns the registered replications with the status (if the replication is active then the value for status looks like Processed 3 / 20 changes). You can use this info to get the replication progress. You can find more info about it from slide 30 here.
We’re in the process of adding guides similar to the one you pointed out but for the CBLite REST API so thanks for your patience and feel free to ask questions here.