That might not work for you, granted, but the amount of bandwidth available between all those ports (20 GB/s in the case of Thunderbolt 2) should be enough to cover most use-cases.
Things like graphics cards use 16x PCI-E 3.0 at this point which is 128Gbits/s.
Thunderbolt IS PCIe, so it's just as fast.. Why should card makers be constrained in expanding the machine to make peripherals small enough to fit inside? If I want 1 solid foot of Disks for my workstation, then so be it. Wire it in over Thunderbolt, and I'm good to go.
20 Gbit/s thunderbolt != 8 drives @ 6 Gbit/s (42GBit /s)
i think a modern raid card can deliver 8gbit/s over 8 PCIe 3 lanes
However i guess you could trunk a few together?