Just to be clear. "Spring" isn't a specific time frame as Spring in Europe isn't the same time as Spring in the USA for example. However, Ivy Bridge-E is expected some time in mid to late 2013. Presumably before Ivy Bridge-E is released there will be an update to the Sandy Bridge-E lineup in the form of the first 8 Core / 16 thread Core i7 3980X Pro-sumer processor.
Anyway, the time frame for Ivy Bridge-E release may match up with Spring in Europe. I'm not sure either way,....
Ivy Bridge-E support doesn't necessarily mean that Sandy Bridge-E support will be improved in OS X but its likely the two will go hand and hand. My concern is that the X79 / C606 chipset has no native USB 3.0 support and motherboards have no Thunderbolt support due to the Intel iGPU requirement. In order to address this there may need to be a new chipset which could mean the older X79 chipset will remain poorly supported.
I cant picture how Intel would provide Thunderbolt support without forcing the Intel iGPU requirement so that becomes a sticking point. Apple could simply provide better support for third party USB 3.0 controllers but there is no way around the iGPU requirement of the Thunderbolt spec.
I'm sure Apple doesn't want to release a new Mac Pro without USB 3.0 and Thunderbolt support,.....they want continuity,....