Cloud Functions / Lambda are great for setting up things such as serverless architecture but they lack a few things necessary for typical "fast data" or stream processing tasks. One could do significantly more with these if they had a method for saving state in a thread-safe manner. I know you can call out to dynamo or the like but an in-memory solution is necessary for any sort of reasonable request rate.
With some state one could implement bloom filters, top-n, cardinality estimations, etc...