That is one of the more stupid mock-ups that I've seen in a while.
If the new system is backwards compatible, then either 1) the new controllers will be used INSTEAD of GC controllers, or 2) there will be a way to use 4 GC controllers on the system. Nintendo isn't going to put two ports for GC games when they are the company responsible for reviving 4-player gaming in the console market.
I'm assuming the "cartridge slot" is supposed to mean "Revolution jacketed disk slot". I was seriously wondering why the illustrator was implying that N64/SNES/NES carts would plug into a disk bay.