devel_variable*() functions missing.

[klonos]

In devel.pages.inc, between devel_field_info_page() and devel_session():

/**
 * Form constructor for displaying and editing variables.
 *
 * @see devel_variable_form_submit()
 *
 * @ingroup forms.
 */
function devel_variable_form() {
  $header = array(
    'name' => array('data' => t('Name'), 'field' => 'name', 'sort' => 'asc'),
    'value' => array('data' => t('Value'), 'field' => 'value'),
    'length' => array('data' => t('Length'), 'field' => 'length'),
    'edit' => array('data' => t('Operations')),
  );
  // @todo: We could get variables out of $conf but that would include
  // hard-coded ones too. Ideally I would highlight overridden/hard-coded
  // variables.
  $query = db_select('variable', 'v')->extend('TableSort');
  $query->fields('v', array('name', 'value'));
  switch (db_driver()) {
  return $form;
}

/**
 * Form submission handler for devel_variable_form().
 */
function devel_variable_form_submit($form, &$form_state) {
  $deletes = array_filter($form_state['values']['variables']);
  array_walk($deletes, 'variable_del');
  if (count($deletes)) {
    drupal_set_message(format_plural(count($deletes), 'One variable deleted.', '@count variables deleted.'));
  }
}

/**
 * After build callback for devel_variable_form().
 *
 * Wrap each variable name in a <label> element.
 */
function devel_variable_form_after_build($form, &$form_state) {
  foreach ($form['variables']['#options'] as $variable => $element) {
    $form['variables']['#options'][$variable]['name'] = '<label for="' . $form['variables'][$variable]['#id'] . '">' . $element['name'] . '</label>';
  }
  return $form;
}

/**
 * Form constructor for editing a variable.
 *
 * @see devel_variable_edit_submit()
 *
 * @ingroup forms
 */
function devel_variable_edit($form, &$form_state, $name) {
  $value = variable_get($name, 'not found');
  $form['name'] = array(
    '#type' => 'value',
    '#value' => $name
  );
  $form['value'] = array(
    '#type' => 'item',
    '#title' => t('Old value'),
    '#markup' => dpr($value, TRUE),
  );
  if (is_string($value) || is_numeric($value)) {
    $form['new'] = array(
      '#type' => 'textarea',
      '#title' => t('New value'),
      '#default_value' => $value
    );
    $form['submit'] = array(
      '#type' => 'submit',
      '#value' => t('Submit'),
    );
  }
  else {
    $api = variable_get('devel_api_url', 'api.drupal.org');
    $form['new'] = array(
      '#type' => 'item',
      '#title' => t('New value'),
      '#markup' => t('Sorry, complex variable types may not be edited yet. Use the <em>Execute PHP</em> block and the <a href="@variable-set-doc">variable_set()</a> function.', array('@variable-set-doc' => "http://$api/api/HEAD/function/variable_set"))
    );
  }
  drupal_set_title($name);
  return $form;
}

/**
 * Form submission handler for devel_variable_edit().
 */
function devel_variable_edit_submit($form, &$form_state) {
  variable_set($form_state['values']['name'], $form_state['values']['new']);
  drupal_set_message(t('Saved new value for %name.', array('%name' => $form_state['values']['name'])));
   'devel/variable';
}

[klonos]

...we have moved to config in Backdrop. So does it make sense to have respective functions, or should we provide deprecated wrapper functions for them?

[quicksketch]

Hm, Backdrop does still have the variables table, even though it's not used in core and deprecated. I'm not much a fan of including functionality for it in Devel.

As for an analogue in Backdrop, editing config files is much easier than manipulating a database table with serialized values. And if you want a UI for editing values, you can use the existing config import UI to modify individual files.