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