I expect a spike on POWER 8 launch, but IVB-EX will make it more difficult, and I still think the long-term trend, irrespective of these cyclical upticks, will be down.
The Unix server market has been shrinking about 15-20% a years since late 2008. Power7 was a huge improvement over Power6 yet it hasn't kept Power sales from dropping like SPARC and Itanium. I doubt that Power8 will arrest Power server sales shrinkage. At best it might drive IBM's MSS within the shrinking Unix server market even higher but that is still not a sustainable business model. IBM has been trying to sell Power for Linux but that is not credible given the economy of scale and great performance for Linux on x86.
OTOH, mainframe (system z) sales seem to have stabilized and every new product cycle generates a large, predictable sales cycle.