Actually it appears somewhat upgradeable; the memory is seated in standard slots and is clearly user-serviceable. The SSD appears to be as well; it may require third-party kit ala OWC (One World Computing) but oh well.
The only two remaining components that may or may not be are the GPU boards and the processor. The system seems serviceable enough so far.
But let's wait for final specs and user guides before passing judgment.
It hasn't been announced, but xenon processors and PCI-E flash storage is typically much more expensive than the Core Processor line or SSD storage since they are almost exclusively marketed towards servers.
That said, disregarding the Apple tax I'm sure Apple gets pretty good deals on their hardware so it is possible that it will be at similar price point as the current line (which was typically regarded as over priced and outdated anyways)
