If the problem to solve here is maintaining a constant distance of the laser from the surface of the resin I would think using styrofoam would be hard to use to do this. The styrofoam would require a minimum fluid volume/resin height before it begins to float, which means it would not be that constant distance from resin print surface without filling the print area with that minimum volume. That means an overhead on the print time. As Synchron points out, the risers and/or guides could get jammed, or at the very least contribute friction and resistance which means this has to be included in the styrofoam's volume and the minimum fluid volume/resin height as well.

What if the styrofoam was damaged? It will inevitably lose mass, again changing the minimum resin height. If the floatation method could be produced by some pressurized structure that would be very hard to damage, the minimum height problem could be solved, and all done without guides, this might work. I'm a little baffled as to how you could overcome using guides and can't quite picture a system in which the volume of resin displaced is constant from start.