Iris Blasi asks:

…

Reading—for avid readers, at least—necessitates an active role not addressed by the passive noun “audience.” The act of reading is different from the act of watching. (So-called) “real” readers inhabit a book and live within it during the reading process.

The publishing…

I have to be honest - as far as umbrella-termed collective nouns go, I think “readers” is fine. It clearly defines who you’re talking about.

Collective nouns serve to more concisely express the intent and/or action of a group. We have “army” so we can ascribe a singular will to what would otherwise be described as “a big group of soliders;” We have jury because it’s better than “a group of people sitting in judgement;” we have “society” as a bullshit umbrella term for a shit-ton of differences and inequalities that we want to ignore while pressuring individuals into codified behaviors and attitudes we believe everyone should adhere to.

Readers is clear. The people who read what you put out into the world. There’s really no need to complicate it.

As far as finding words to define niches or readers with specific interests, I’m gonna go ahead and play the “identity is dead” card. If you start coining terms for every single subgroup, eventually it will get narrowed down to a single person in each group, and you might as well say,
“I’m writing this book for Steve” because chances are Julie, Aiden and Martha may have some things in common with him but won’t exactly fit your definition for the literary niche you’re carving out.

To assume we can start coining more specific collective nouns for subgroups of readers is to probably vastly oversimplify who those individual readers are. You might get a few gems that stand the test of time, like Trekkies or LARPers as subsets of nerd, but generally it’s not going to do a whole lot of good.

And honestly, it’s also just lazy. Use your critical thinking skills and thoughtfully define the group of people you want to reach. It’ll make both the project and the product more interesting, and allow for actual dialog.