I have a feeling their chip supply/manufacturing capacity is being converted to S2, my guess is that at this BTC price the shipping cost is starting to eat to much into their S1 profits to be worth it.
Most people think the S1 and the S2 use the same chips. My bet is the boards are almost the same as well, just undervolted.
I agree. Price means everything. Ship more, do it cheaper. Printing those proven 55nm chips is very cheap now. Generally mining board like that wont cost too much when your doing 500 000 or more. If chip is your own. Bitmain must aim shipping S2 miners huge amounts.