Expresscard also exists as a hotswappable version of PCIe for laptops. It's only one lane, so even the modern laptops with PCIe v3 have dismal bandwidth compared to USB3 or Displayport.
Surprise unplugs aren't great. On windows you can safely eject a GPU from your laptop with the taskbar icon.
Compared to thunderbolt it's an order of magnitude cheaper.
- no power
- limited ASPM support, no CPM support
- much larger (36 pins)
additionally, I imagine user experience is worse due to most systems only enumerate at startup and dont handle surprise unplug well at all.
https://pcisig.com/specifications/pciexpress/pcie_cabling1.0...