TYPO3.Flow

When configuring a jsonView for a domain object, the '_descendAll' configuration is currently not taken into account, leading to the need to configure all properties for traversal.

The part of TYPO3\FLOW3\MVC\View\JsonView::transformObject line 199+

                if (!is_array($propertyValue) && !is_object($propertyValue)) {
                    $propertiesToRender[$propertyName] = $propertyValue;
                } elseif (isset($configuration['_descend']) && array_key_exists($propertyName, $configuration['_descend'])) {
                    $propertiesToRender[$propertyName] = $this->transformValue($propertyValue, $configuration['_descend'][$propertyName]);
                }

should be

                if (!is_array($propertyValue) && !is_object($propertyValue)) {
                    $propertiesToRender[$propertyName] = $propertyValue;
                } elseif (isset($configuration['_descendAll'])) {
                    $propertiesToRender[$propertyName] = $this->transformValue($propertyValue, $configuration['_descendAll']);
                } elseif (isset($configuration['_descend']) && array_key_exists($propertyName, $configuration['_descend'])) {
                    $propertiesToRender[$propertyName] = $this->transformValue($propertyValue, $configuration['_descend'][$propertyName]);
                }

A further nice-to-have feature would be a real _descendAll configuration that just carelessly descends all objects, though it probably should still deal with recursion of domain objects or stop at a specific recursion depth.
Something like an int configuration _recursionDepth would work:

                } elseif (isset($configuration['_recursionDepth']) && $configuration['_recursionDepth'] > 0) {
                    $configuration['_recursionDepth']--;
                    $propertiesToRender[$propertyName] = $this->transformValue($propertyValue, $configuration);

On a side note: The current implementation for configuration settings behaves differently for arrays / ArrayAccess objects and other objects.
While for arrays, _descendAll overrules _only and _exclude settings, for an object _only and _exclude overrule _descend (and with the patch above also _descendAll).