There are several other threads about updates - search the forum for "Haswell".
Intel is updating the CPU used in the MP6,1 this fall. The new CPU will use the "Haswell" architecture and be called the Xeon E5-1600 v3 and Xeon-2600 v3 series - the current MP6,1 uses the "Ivy Bridge" "v2" series.
A refresh is definitely possible - the stars have aligned.
ps: I agree with Umbongo in the following post, volume production (as in "in stock at Apple stores") of the Haswell update is unlikely by the holidays.
It isn't a yearly thing, no. The launch date for new CPUs is this quarter, most likely September, but shipping in quantity by November and obviously it hinges on that. I'd be surprised if Apple released it in 2014 though, and even if they did there may be supply problems again.
I wouldn't suggest waiting on new models unless you are willing to wait until March 2015 to get one in your hands, and I base this on my experience of every previous Mac Pro and workstation launch since the move to Core 2.