I bet they try something different this time than just an extension... maybe some sort of "brand icon" exemption that exempts any character who is strongly associated with a brand from copyright expiration. They probably sense that continuous extension isn't going to work forever.
The logo for Disney Animation before their movies is a clip of a few seconds of Steamboat Willie. I expect them to lean even more heavily on trademark protection once the copyright expires.
Besides, it's not like the copyright on the old theatrical shorts is that valuable. The real interesting stuff will be in the 2030s when the feature-length films start entering the public domain...of course by that point you probably won't be able to find any non-DRM video, if current trends continue.
My intuition tells me that those of us who care about freedom will find a way to seep through the cracks of any wall attempting to destroy it. I agree the current atmosphere is bleak, but let's not give up so easily.
I just built the Steamboat Willie LEGO set. Was wondering what prompted that particular curiosity; copyright extension leveraging seems a plausible motivation.
That would probably be a violation of Berne Convention because brands are national constructs and require registration and convention requires copyright to exists independently of national borders and without registration.