Cursors are much more common in the non-distributed database world which is also most often disk IO driven, where Couchbase is much more streaming and memory oriented. In that environment, you have a stateful connection which is iterating a result set that may be disk buffered.
While it’s possible that we might add something akin to cursors on the cluster in the future, that doesn’t exist today so there’s nothing to expose in PHP.
For many situations, the use of OFFSET and LIMIT in queries is sufficient.