Given that the Amazon cloud is such a huge consumer of Intel's X86 processors, even using Amazon-tailored Xeon's, it's surprising that Amazon chose Xilinx over the Intel-owned Altera.
These Xilinx 16nm Virtex FPGA's are beasts, but Altera has some compelling choices as well. Perhaps some of the hardened IP in the Xilinx tipped the scales, such as the H.265 encode/decode, 100G EMAC, PCI-E Gen 4?
Stratix10 (the large, Intel 14nm family) was delayed, delayed, delayed, and delayed some more. Last I heard it was supposed to be in high-prio customer hands by end of 2016, but unclear if that meant "more eng samples" or the actual, final production parts. Either way Xilinx beat them to market by approx 3-6 months AFAICT.
These Xilinx 16nm Virtex FPGA's are beasts, but Altera has some compelling choices as well. Perhaps some of the hardened IP in the Xilinx tipped the scales, such as the H.265 encode/decode, 100G EMAC, PCI-E Gen 4?