AMD has confirmed that Fusion needs a new set of development libraries to make
this device posible. The chip conbines CPU libraries with the GPU libraries and
therefore these two teams had to sit together and develop a new set of instructions
to be able to make such a chip.
There are many obsticles but when you integrate you have to inovate and 10+ years ago mathematical cooprocessor was an external chip and for years now it is the part of the CPU.
The big question is how will make fusion someone like TSMC or AMD itself in Fab 36 but we have more than a year to worry about that.