TL;DR: This Gist sketches out an API for providing a means of managing inheritable indexing configurations in ActiveFedora. Primary motivations are (1) to avoid (for most purposes) putting indexing logic in an overriden #to_solr method, and (2) to make it possible to introspect a model's or instance’s indexing.
An earlier version of this idea was kicked around on IRC, and I've refined it significantly since then, mainly to accommodate the current property indexing API (from ActiveTriples). Originally, I just aimed to deal with indexing calculated values (basically model methods, as opposed to attributes or properties which already support indexing), for which one currently has to override #to_solr.
Essentially, I wanted to be able to do this type of thing on a model:
# Stupid example