We should look at updating to PHP 7.3 once 7.3.1 is released and we have upgraded to mediawiki 1.32 T3794 .
PHP 7.3 hasn't been released yet. Isn't this a bit premature as we don't have a release date or even knowledge of a release at all?
7.3 has now been released
With this upgrade we now have a running luasandbox that i Buildt.