I've always wondered if they would introduce a new GPU but keep the same CPU as a baseline. That way they can catch any trends in regards to DX11 game adoption, 3D, full HD etc and still be future proofed so a console bought in 2011 would still be relevant in 2016. Sort of how the gameboy and gameboy colour played the same games at first but after about 3-4 years the upgraded 360s would diverge and play only exclusive content or downgraded next generation content (next generation meaning 2014/5.)
At this point it doesn't get much cheaper to produce an older model GPU vs a newer more efficient model, the memory costs the same whether they've got 1GB or 512MB, they've got to rework the GPU anyway and they can grab about 50 GB/S memory bandwidth for about no extra charge. It does seem like a possibility.
Tease.
Essay Pro