I think, according to what members say that they receive i used S4 gears full of dust, and also the huge sale that bitmain need to do with the current products. this only mean that they replace their farm gears with some thing more powerful and they need to sell all the old stock.
May be after a while when they use this new product and get some decent profit from it then they will release it to the public.
i've a feeling that doing this is going to put a stop to the cogs. While other h/w manufacturers are shipping more efficient miners from stock, do you really think bitmain would halt sending out their most profitable rigs to customers and let other companies take the market share.
and just because they can mine themselves with their new gear, does this not mean they will be stuck in the same position when they do open it for sale? other manufacturers will be a jump ahead.
my opinion is that S5 isn't finished yet and as soon as it is, they will want it out on sale to customers.