The very fact that this is a single CPU machine indicates it's not a pro level workstation.
Sure it may be 12 core, but it COULD be 24 core.
Basically it's the desktop headless mac that people have been asking for for years. It's not a disaster, but the limited upgrades (only 4 memory slots and 1 CPU) clearly indicate it's not a pro level workstation.
Forget the thunderbolt vs. internal crap, the above is not upgradable outside the box.
I am however glad that they at least put effort into developing it, and the engineers came up with some cool stuff, I just hope in the future they will go bigger for performance.
It's not what it will be (faster ram performance, bandwidth, etc) compared to now, it's what it COULD have been if they had gone dual CPU, more memory slots, etc.