I think you smacked the proverbial nail straight on the head there! Though I still question why they went through the design process for the S4+ (they look to have flipped the chips like they did with the S5), I suppose since the S3+ (sold only in China) was already about, they deemed it feasible to milk the last ounce out of their older chip seeing they were rushed to market with the BM1384 (S5) chip.

On the whole, that would be understandable, but then the pricing at that efficiency (compared to an existing and available S5) is mind boggling. I can not think of bitmain caring more about the network (and diff rises et al) more than their bottom line. On the face of it, the dev costs for the S4+ are down the pan as no one in their right mind would buy the S4+ out of China! So that leaves the option that this was built (and is being targeted) for their hosting service! Neat trick there bitmain, but it will only come off if the power costs borne by the user are at or less than 8 US cents.

Saying that, the S2 upgrade kits must be a matter of logistics now .... surely!