The GitHub link works!
My experience so far (commit a1abcc96b1fca33caee172b31eb09d93e288c0bd):
SDK not found warning
When I import the project, a dialog appears:

After confirming the active selection (there are no other selections), the import completes. Question: is this warning harmful?
_sdk_work wrong path
When I click Build in Quickstart Panel, the console shows this error
*** No rule to make target 'C://_sdk_work/repo-directory/iot-rpk/utilities/fsl_assert.c', needed by 'utilities/fsl_assert.o'.
I grep'ed for _sdk_work and found a reference in boards/rapidiotk64f/demo_apps/ble_sensors/.project. In this file under /projectDescription/variableList key, I changed both value to $%7BPARENT-4-PROJECT_LOC%7D, and the code compiles.
Uploading boards/rapidiotk64f/demo_apps/ble_sensors/Debug/ble_sensors.bin to the kit works.