Is `dpkg-reconfigure --all` still available in 16.04?

Not equivalent, but probably what you are looking for if you want to be sure, everything is at least somehow configured:

dpkg --configure -a

You can try this script:

    for i in `dpkg -l | grep '^ii' | awk '{print $2}'`; do
        echo $i; sudo dpkg-reconfigure $i;
) 2>&1 | tee dpkg-reconfigure.log

It reconfigures all installed packages and saves the log to dpkg-reconfigure.log file.

No, dpkg-reconfigure on 16.04 (but also on 15.10) does not have the option --all any more, although it was present in 14.04 (not sure about 14.10).

You could have verified that yourself by checking the command's manpage:

man dpkg-reconfigure

On a 16.04 (or 15.10) system, this manual page will not list an --all argument, while on 14.04 one is present.

If you don't have those systems at hand, just read the online manpages: 16.04 - 15.10 - 14.04
(note for future readers: if one of the linked releases has reached end-of-life by the time you read this, the link will redirect to the latest release's manpage instead of showing the old, archived version)