Problem/Motivation
One major piece of functionality from the D7 Entity Reference module was left out entirely in #1801304: Add Entity reference field: the ability to render exposed views filters as a select list of available entities.
Proposed resolution
Generalize the taxonomy module's TaxonomyIndexTid plugin to be available for all entity reference fields.
Remaining tasks
User interface changes
The UI from D7 will be a good starting point:
API changes
TBD