Hi Miles,
Sounds like a very interesting project! I don't have any firm answers for you, but can instead perhaps point to some possible inspiration. First, a couple slide decks that might hold ideas:
This deck is a bit older so some of the source sites may have changed since, but it includes some examples of the various creative ways that people have use AtoM to meet their institutional needs:
In particular, I was thinking that perhaps the Beaton Insitute's use of static pages (to create topical landing [pages as a way into dispersed collections) and access points (to unite those disparate topics) could inspire some ideas.
Secondly, I don't know if there is any particular slide in here to highlight for your use case, but it's often handy for newer community users to see this roundup:
It's a very very different case, but in Canada, the National Centre for Truth and Reconciliation has also had to accommodate entities that don't match exactly to AtoM's default use. For example, they are using the authority record module for both Schools, People, Communities, etc... but also more generally , for Events that don't fit neatly elsewhere. They have done this by adding a new Event entity type to the Actor Entity Type taxonomy, so that users can facet the results by that type (and they can include faceted links and buttons on theme or static pages). See:
If you look at the options available in the dropdown Browse menu, you can also see that elsewhere they have used different access points on records, and then customized the browse menu to provide faceted results directly (see for example the difference between the Historical Photographs and Contemporary Photographs links in the Browse menu).
Finally, it's a much more expensive option, but the Glasgow School of Art has integrated its AtoM site with a comprehensive custom theme and a CMS (like Wordpress or similar), and users flow freely between the CMS and AtoM as they browse, allowing the site maintainers to provide all kinds of different ways into the holdings. See:
You can explore more example AtoM sites from our wiki:
Hopefully others might answer as well and share their own examples!
Cheers,