In my opinion, adding more array_*_recursive() functions should be
avoided. Instead it might be useful to have array_flatten(), so
one could do

  array_filter(array_flatten($array), $callback)
  
Then again, defining array_flatten() in userland is quite simple:

  function array_flatten($array) {
      return array_reduce($array, 'array_merge', []);
  }

Anyhow, with regard to the mentioned issue of empty arrays, it
seems indeed best to leave the implementation for userland.

According to my comment above, I'm closing this ticket. If anybody
still thinks it would be a useful addition to the standard
library, please pursue the RFC process[1].

[1] <https://wiki.php.net/rfc/howto>