Get a list of revision IDs for any given entity?
Figured it out. I'll leave it here because it might be useful to someone down the road.

You can use this function to get a list of all revisions ids for any given entity.

/**
 * Get a revision id list for a particular entity.
 */
function get_entity_revision_list($type, $entity) {
  $info = entity_get_info($type);
  if (!isset($info['revision table'])) {
    // If this entity does not track revisions then return FALSE.
    return FALSE;
  }
  if (!isset($info['entity keys']['revision'])) {
    // If for whatever reason a revision table was defined, but no revision key
    // then also return FALSE.
    return FALSE;
  }
  $revisions = db_select($info['revision table'], 'r')
    -&gt;fields('r', array($info['entity keys']['revision']))
    -&gt;condition($info['entity keys']['id'], $entity-&gt;{$info['entity keys']['id']})
    -&gt;execute()
    -&gt;fetchAllAssoc($info['entity keys']['revision']);
  return array_keys($revisions);
}