This is still false.
The copyright holder who places something under the GPL gets to decide what they can do with their own code, including mixing that with closed source.
As has already been proven, differences in interoperability between the plugin and host may or may not allow 'combining'. The FSF has opinions on that, but ultimately, for a mechanism designed to allow combining, the copyright holder is the one who gets to device.
And has already been proven, exemptions to this can be made by the copyright holder.