For anyone needing time to switch plugins, or anyone who really needs W3TC but needs to make it secure .. this small plugin will stop all access to the W3 total Cache (Version 0.9.4.1) XSS support page,

just install (preferably as mu-plugin) and you are all done.
https://github.com/ramonfincken/w3tc_deny_supportpage Instructions are in the README.md file

W3TC will continue to cache your site, and you will have some "breathing time" to search for an alternative caching plugin.

Note: I still think it is time that W3Edge releases a fix for this and many other things as well (PHP 7 support for instance).