Even nVidia took several years to make the Tegra epic fail into a reasonable win. The first generation lost every design win except for the Zune, and the second generation ended up ramping in volume about a year later than nVidia said it would.
AMD might get more from ARM than nV. I could see and ARM processor integrated into AMD's current fusion design. It would make a wider power envelope. When the ARM processor is enough, ... The way most people use desktop, dtr, etc., the power savings would help. Probably get down below SB on low power, and match performance albeit at higher power consumption, when needed. A long way off, if at all.