This feature request relates to version 4.0.0
When mysqli is disabled on the server, calling index.php from a fresh install resulted in an error message saying that mysqli is not enabled. I suggest to mention in this error message that in the config.inc.php file mysqli can be switched off as an alternative. For enabling mysqli the server administrator rights are required while for editing the config.inc.php this is not the case.
See also screenshot below (in Dutch, The Netherlands)