The contrib Entity API provides a way to create bundle plugins without a config entity: https://www.drupal.org/node/2817751.

However, from what I can tell, those bundle fields are not exposed to views – only the base fields. When creating a view that is for a normal entity type, e.g. node, the additional fields appear to be added in Drupal\views_ui\Form\Ajax\AddHandler::buildForm() at line 82:

$  options = Views::viewsDataHelper()->fetchFields(array_keys($  base_tables), $  type, $  display->useGroupBy(), $  form_state->get('type')); 

When creating a view from bundle types created via the bundle plugin type, the bundle fields are not added to $ options.

What needs to be done in order to expose those additional bundle fields?