Why not, its just a test board and there's plenty of board space. For the retail boards you just don't dont drop PCI-E connectors through and leave them as empty connections.

I personally would have preferred the chips to be centralised and squashed together more so we could have used standardised PC heatsinks cooling all 4 chips. 350W can be done with one higher end air heatsink or basic 120mm watercooling. I think its time we moved away from these strange aluminium blocks with obscene fans to make up for the low surface areas.