Codesigning is only a requirement for app bundles (i.e. native GUI applications), not all executables. The Twitter link indicates that you can still right-click an application, choose open and agree to let it run (this is only necessary the first time you run it), the current beta just removed the Download Apps From: Anywhere option. As of El Capitan (or maybe even Yosemite), OS X automatically changes the setting from Anywhere to App Store and identified developers after 30 days (there are extra command-line hoops to jump through to disable the 30 day expiration).

I'm in favor of the change as long as the contextual menu Open option remains.