It's not capable of guaranteeing complete synchronisation of things.

I'm even working on (in my part time) a filter plugin that quickly recognises whether a reply post references a whitelisted identity, by building filters out of posts made by the user - for the purpose of caching first level replies to posts so the relay has it immediately.

I'm going to be using bloom filters to build a recogniser, not sure how the state is going to be stored but probably replaceable private events for the filter itself as a virtual user. 

 just forgot my second point: compact, addressable merkle trees let you guarantee full set membership discovery, assuming that the user didn't post them to a relay not known by the one trying to find it. But it can know the ID, and it can know the set of a given batch of them that have been bundled into a tree. 

 also, yes, i have read the negentropy documents, and i have been working with strfry. why in the lord's name did they build it using perl and c++? It's not 1998 lol.