Zend framework was already added in last release 2.1.8.683 ;-)
But to be honest, there is currently no difference between "Without MVC" and "Zend FW".
In case of Symfony framework, ORM Designer uses different search paths in automatic importers. But in case of ZendFW the same algorithm is used when no MVC is selected as same as when ZendFW is selected.
The main reason why we added ZendFW is because a lot of users was consufed if they can use ORM Designer if they're using ZendFW.