I think they make use of the fact that individual lines are updated on the camera by the light and can subsequently be read out. If it were a camera with global shutter, chances are it could not be configured to update lines as fast indivually. A global shutter design copies each pixelsite or line into an indiviual buffer when the "shutter" signal is triggered. This happens in parallell.

I'd say these high framerates on Raspi cameras definitely is an artefact of the rolling shutter design in these cameras.

Maybe one could get even higher framerates by hooking the analog part (or very close thereafter) of the rolling shutter camera up to something else, but I don't see how.

Correct, a CMOS sensor with a rolling shutter looks and handles a lot like a piece of DRAM. Pixels are arranged in rows and colums; capturing a frame works just like a sequential read through a DRAM array. The nominal frame-rate at a given resolution is set by the read-out speed of the array, so reducing resolution increases speed almost linearly.