File this one under "probably not a problem, probably." Rumor has it that while AMD's Zen processors are on track and "have a satisfactory yield rate," the chipsets for them, designed by Asustek subsidiary ASMedia, are having issues with signal quality on USB 3.1 connections. Specifically, Digitimes says "USB 3.1 transmission speeds drop dramatically as circuit distance increases."
This problem would require motherboard vendors to use additional supporting hardware to maintain USB 3.1 performance, increasing the materials cost for affected boards. Digitimes claims that AMD is considering supplying third-party retimer and redriver chips to motherboard vendors along with the chipsets. As usual, Digitimes did not give any source for the statements it cites.
Earlier roadmaps including Zen mentioned a "Promontory" chipset, and we'd wager that's the chip that's been outsourced to ASMedia. AMD declined to comment on "customer-specific board-level solutions," but it said that it was pleased that Zen is on track. On the other hand, ASMedia specifically denied the rumor, remarking that its "product's signal, stability, and compatibility have all passed certification."
Intel's Sandy Bridge platform, which was a similar step forward for the company, also faced an issue with its chipset design. Assuming the rumor is even true—it is, after all, just a rumor—this certainly sounds like a relatively minor issue. According to other rumors, the Summit Ridge processor has USB 3.0 and SATA on-die, so faults in the Promontory chipset may simply be swept under the rug.