I asked OWC about memory for the new 2013 Mac Pro. I was hoping to hear that 128GB would be possible immediately, but at present this looks doubtful:
We already have 1866 MHz upgrade kits for up to 64GB in the new Mac Pro lined up and ready.
Upgrades beyond 64GB will be dependent on specifics related to the Mac Pro and/or memory device availability meeting Mac Pro 2013 model requirements.
While the Intel Xeon Processor and Chipset utilized in the new Mac Pro is capable of addressing 128GB (actually well more than that), still remains to be seen what will be 'allowed' within Apple's implementation and EFI firmware control.
Apple’s best = handicapped machine
Apple shows its disdain for needs of professionals by offering a Mac Pro with only four memory slots; serious workstations should have eight or twelve memory slots. A Mac Pro is the top of the line machine after all. From Apple’s marketing:
You refuse to rest until it’s the best it can possibly be.
Four memory slots is the best it can possibly be? It is unbelievable really. How do I edit my big Photoshop files without virtual memory paging even with 64GB of memory? What about huge data sets for scientific computing?
On that topic, how about not just a single internal PCIe SSD, but at least two? The idea of “redefining 'best'” takes on a whole new meaning.