I was checking Micro Manager, and they provide binning by capturing frames and Live View in monochrome, besides the camera not being set to use this Picture Style.
Using it's Continuous (Live) View, with my 700D and MacBook Pro, I managed to get 10 FPS @ 960 x 640 8-bit, and binning 2x2, 4x4, or 8x8 didn't affect FPS.

Even only available in BW, I think monochrome binning via GPhoto would be valuable for Plate Solving speed boosting, and also for auto guiding, since it improves the signal to noise ratio (SNR).
But, unfortunately, if not supported by the camera firmware, binning won't increase the frame rate of the Live View, nor decrease readout/download time.

The only other implementation I know that features 3x3 binning in color is "crop_rec on steroids" module for Magic Lantern , and the "Crop mode recording (crop_rec.mo)" module (also for Magic Lantern) that enables 3x zoom . Both modules seem to work only for SD video recording (raw/h.264), using "MLV Lite movie recording" module for Magic Lantern .

So, it would be possible to have 3x3 binning and 3x zoom by hardware, but it would require an specific Magic Lantern module for Livew View and still captures, and its support by GPhoto.

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