Do prefect 2's blocks have any sort of locking functionality? (imagine a queue-like block with some flows adding to it and others removing, how could they maintain reliability that no item gets lost?)

That’s a very interesting question @Nathaniel Russell! We don’t currently have any locking functionality for block documents so we can’t guarantee that data will not be overwritten if multiple flows are writing to the same block documents. If there’s enough interest in functionality like this then we can prioritize development of this feature. Just out of curiosity, do you have any particular block types that you are updating from multiple flows?