Look at previous boards and the board in the test - they're almost bare.
Are there reference designs or public information regarding any other than the 55nm bitfury generation? It would be a waste not to put a heatsink on that chip - or immersion cool it, like they do themselfs.
AFAIK no ones even benchmarked a 28nm chip in the wild, every machine must have been sold under a solid NDA or mandatory purchase order. Its pretty crazy if you think about it, 1000s and 1000s of BF3500s and BF4500s and not one has ever been 'tested'.