Using a single partition in Kafka is similar to using a single Node in NiFi to maintain order. The enforceOrder processor is a great new addition for enforcing order of FlowFiles, but it will only enforce orders on those FlowFiles that reside on the same node in a NiFi cluster. So if you are trying to enforce processing order of FlowFiles across numerous nodes, this processor will not do that. You would need to get all FlowFiles for which you want to enforce order on to the same node before using this processor.
I don't fully understand you entire use case, but a couple other processor you may want to look at include wait ad notify processors. These are also new in the latest HDF 3.0 and NiFi 1.2.0 releases.