Canon has filed a patent at the USPTO for a new mirror box design. This new mirror box adds speeds and a reduction in bounce.
There are a lot of parts to a mirror box assembly, and it's easy to see how the remove of this complex system could greatly reduce the cost of production and increase margins for camera bodies, but we're not ready to be rid of it yet.
It's obvious that an EOS 7D Mark III and and EOS-1D X Mark III will remain “mirror slappers” for their next iterations. We should also expect to see improved FPS in both camera bodies.