ALL the 3 PCIE connectors are needed to be connected to power supply on each hash board .... since it is based on serial power solution and there is no DC/DC inside the miner.
Those two statements are unconnected and don't make sense as a justification. If each board can still only be powered by one PSU due to cross-loading, then each board's 3 PCI-E connectors are still connected. While we don't have any high res images to see if we can see tracks, each of the PCI-Es is still in-line and *appears* to be powering the same plain. That agrees with the cross-loading argument which would mean that each PCI-E is the same as the next, meaning the only limitation is maximum load and not because it doesn't have DC/DC.
i tend to agree with this. if each board is drawing <400W you could provide that with only 2 cables. my guess is that it does two things:
1) prevents people from burning up cheap 18awg cables (that are limited around 150W)
2) slightly better balance of power distribution so the connector or copper traces dont fail
I absolutely understand that the official line will always be use all 3, however the technical explanation as to why you must use all 3 didn't really make sense.