Hi @nickandre, and welcome to the club!
The usual setup with the HQ camera is to use an intermittent film transport, either by misusing an old Super-8 projector or by using an own design for transporting and stopping the film precisely.
If the mechanical precision is not good enough, usually a computer vision algorithm is utilized which uses the film sprockets for frame alignment. Since the sprocket which defines a specific frame position is by standards 2 film frames away from the film frame currently scanned, that is only an approximation - but it works ok.
With this intermittent film motion, it is possible to scan several different exposures of the same film frame. This enables various approaches to extend the dynamic range of your camera sensor - the color-reversal nature of old Super-8 film stock requires a dynamic range which exceeds most available camera sensors. The HQ camera features 12 bit per color channel at most which gives you quite some sensor noise in the dark areas of the film.
Another scanning approach uses a continuous film motion, with a short enough exposure/flash time to freeze the image of the film frame sufficiently sharp on the sensor, despite the film movement. This type of scanning avoids the constant movement/stop for the film material and is potentially sligthly safer for old material. You most certainly need a computer vision algorithm again to align the scans of each film frame with each other.
With continuous motion, there is not really a chance to do any multi-exposure easily.
As far as I know, a film scanner based on a line sensor has not been described here on the forum. The only one which comes close to this might be the Nordmende Colorvision CCS (here is the service manual, and here one which is currently on sale). Well, that’s actually a flying spot one, not a line-based scanner.
These kind of machines were used because at that time there were no viable image sensors available for that task. So the approach you are suggesting has certainly a kind of retro touch to me. Could it be realized?
Probably, with quite some efforts. The current RP approach (libcamera) is not tuned to such an approach. Very close to what you want to do is the work of HermannSW at the RP camera forum on high speed captures utilzing a cropped area of the image sensor - you might want to have a look at his various posts.
Be aware that the HQ sensor is a rolling shutter sensor - this might create issues if the scan direction is not chosen appropriately. Also, you trade in the precise 2D pixel alignment of the sensor with a 1d line scan where the alignment in the orthogonal direction depends on the mechanical aspects of your film transport system. Pushing two subsystems of the envisioned design - the libcamera software interface and the mechanical design of your scanner - to the limit would be two challenges one can simply avoid by using the HQ sensor in its normal mode, that is: taking always a full frame image.
Note that there is a global shutter camera available from the RP foundation, albeit with a lower resolution than the HQ sensor. Have a look around this forum - you will find a lot of different approaches towards digitizing film, including scan results of the different approaches.