..my observation that they would need to structure rep different for different #hashtags, which is no where in the whitepaper.
Sure it is. That is explained across several sections in the white paper.
2.2.2
2.2.7
and more in 2.7 - within pi-calculus.
One thing that might help, is to understand how other terms are used instead of the perhaps more familiar "hashtag". It is just a content identifier. You will find this represented by other terms, like "channels", "syntactic entities", or terms specific to pi-calculus like "persisted queues", or even the word "network", as this does not apply to "gods-eye" perspectives here - so these sub-groups are most typically defined by a topic, or keyword.
Content delivery is one of the true innovations of Synereo; it is baked into it deeply. REO functions with it, and based on it.