Sure I know, GCam pioneered this years ago. But all those frames are merged into one which is written as a correct scene-referred DNG with the usual dimensions

Sure I know, GCam pioneered this years ago. But all those frames are merged into one which is written as a correct scene-referred DNG with the usual dimensions and the CFA pattern, as if it was taken by the sensor directly. Which is what GCam and every other app do. They don't write gigabytes of RAWs for a single shot. (although some apps do have that option, within the hardware capabilities) And all this has nothing to do with manual astrophotography, where you ditch computational apps, use a mount and shoot actual unstacked raw sensor frames with several seconds exposure each, interleaving them with dark frames, and do the computation yourself with the dedicated astrophoto software which is far better than any app if you calibrate the sequence and do the math correctly. Every phone is capable of this.