It's actually even more restricted than that. The E3-1200 V5 series Skylake Xeon's that came out last month are in the "server" line, but do not support AVX-51

It's actually even more restricted than that. The E3-1200 V5 series Skylake Xeon's that came out last month are in the "server" line, but do not support AVX-512. I think it's presumed that none of the Greenlow generation will support it, but that the Purley generation that follows will. So far, my limited experience with Skylake would say that performance gains will be small. If you are buying a Skylake laptop, it should probably be for the increase in battery life rather than hopes of significantly higher speeds.