The MI8 is the "Radeon Instinct" - aka R9 Nano @ "<175w," available in 8X clusters. The Mi25 is presumed to be Vega with AMD announcing it as the "Falcon Radeon Instinct Cluster with 16X Radeon Instinct MI25 @ 400 Teraflops." I suspect nVidia likely went with their 32X cluster to top the "Falcon Radeon Instinct Cluster." Last year AMD said '1H-2017' for availability --- likely to coincide with the release of the Naples enterprise platform.
Not sure how Chipzilla will respond with the "Phi" as they are unlikely to stand-pat with their "competition" BUT they do seem to be lagging in FP16 ...