I was reminded of this by both the Manual Rotator helper and the excellent Astroimaging Planner. I’m sure this would be helpful to a lot of people if built into the On-The-Fly panel.
Would it be possible to take the idea behind the Rotator helper and, instead of displaying the Rotation angle, display a mosaic comprising of nine parts of an image in a grid. The stars in each part to have a circle around each stellar centre plus a line going through it representing the angle of elongation. Controls could be exposure time and magnification (of all segments together). Perhaps in the centre frame have a dial indication showing both direction and magnitude of the average elongation and, right angle to, direction as an enhancement (just thinking aloud really).
A friend of mine developed something similar but he didn’t have much time to make it dynamic enough - it processed images as they were written to disk and had a bit of a memory leak issue which was a bit frustrating. I could see if I can get hold of some of the code for calculating stellar centroids and direction of elongation if that would help.
Keep up the great work.