Very unlikely to happen. Intel has been in the past threatened with sanction, and the FTC settlement (aside from being unable to substantially alter PCI-E for another year at least) only makes allowances for Intel's PCI-E electrical lane changes if it benefits their own CPUs - somewhat difficult to envisage as a scenario. Disabling PCI-E would require a justification that would suit both Intel, the FTC, and not incur anti-monopoly suits from add in board vendors (graphics, sound, SSD, RAID, ethernet, wi-fi, expansion options etc.)
Bear in mind that when the FTC made the judgement, PCI-E's relevance was expected to diminish, not be looking at a fourth generation. It's hard to make a case for Intel pulling the plug, or decreasing PCI-E compatibility options when their own server/HPC future is tied to PCI-E 4.0 (and Omni-Path, which has no more relevance to consumer desktops than it's competitor, Mellanox's Infiniband)
Performance/Power might be a juggling act depending upon which target market the parts end up for, but Nvidia released numbers for Pascal at SC15. ~ 4 TFLOPs of double precision for the top SKU (presumably GP 100) which probably equates to a 1:3:6 ratio ( FP64:FP32:FP16), so about 12 TFLOPs of single precision.