@ThantiK , you raise a good point, but one that I anticipate can be solved in at least two ways. Let me rhetorically ask you: how are overhangs created with extrusion-style printers? Two common solutions are to print one layer slightly overhanging, but still touching the lower layer, hoping that the upper layer is sticky enough to adhere without falling off; and printing a second material simultaneously to act as a support material, which can be later removed.
Both of these approaches can be used in the 3D laser printer. The substrate particles may be smaller than your typical filament, but they are still sticky coming off the drum, and can still stick to a lower layer even if they are only partially stuck to it. Further, the drum you see in the GIF is one of about 3 or 4 that can be arranged around the circumference of the center vertical. Thus, 4 different toners can be laid down in quick succession for every revolution of the spindle. If just one of those toners is a support material, this leaves 3 other toners to play with color, or material properties of the build. This is a significant improvement over the current state of the art.