The first GPU meets CPU product will as expected be a Multi chip module. It is the easiest way to make this rather hard transition.

The second generation fusion might actually be a totally integrated chip and this will eventually happen. Just remember the time when a floating point unit was a separate chip and this is the direction you should be thinking for fusion-like products.

First generation will have two separate dies on one chip, while the second generation might result in a CPU getting a GPU on its die. The best way to think about this is that this multi-core CPU will get one or more additional cores that will only take care of graphics.

AMD still has to launch a first fusion codenamed Swift to go for the next level.