Hi there,
So I was able to get it going after a few cups of joe and this late night.
works with both GDB command line debug and with PlatformIO. The trick was NOT to use the OpenOcd builtin to PLIO. Once I set up the generic OpenOcd and the Device manager had the driver for the CMSIS-DAP device (interface 2) as none WinUSB.sys Zidag changed that and BAM! bob is your UNCLE debugger! 
I’ll post a video in action but it’s fast , runs the 921600 baud, flashing is turbo quick.
here are the OpenOcd, GDB and PLIO snaps. target was a Xiao Nrf52840 Sense. Single stepping like a BOSS! 
samd21 and Nrf52840 are verified!! so ESP32"s on deck…
HTH
GL 
PJ 
If they can make this inexpensive everyone will want one. 
- I can see User mode: press a ONE button , unbrick a Xiao. (restore the Bootloader)
- I can see Maker mode: “advanced menu” add your own custom ,hex,bin, uf2 files.
- I can see Developer mode: ANYTHING GOES!!!
Ok Seeedineers get Cooking!