For the master branch, we obviously still need Zend tests enabled; however, for the wmf branches of MediaWiki and extensions the Zend tests may be a superfluous burden.
I kept them around because mwscript is still bound to Zend PHP5 ( T146285 ) which was in reaction to T132751: "Elastica: missing curl_init_pooled method" due to mwscript job running with PHP 5 on terbium.
So triggering the PHP5 jobs might cover the corner case of code being run as maintenance script and we have a lot of it: job runners, getting all wikis configuration etc.
But maybe I am over paranoid and we could just drop them. Though I would still love to see T146285 to be finally fixed.