It’s not a slicer problem but a firmware one. The slicer tells the printer something like “G1 X30 Y10 E5” and it’s up to the printer firmware to figure out how to move the X axis 30mm, the Y axis 10mm while extruding 5mm of filament. Given the fact that the X kinematic here are identical to a bed slinger, just with no end stops, Y and Z use kinematic similar to a CoreXY setup, this shouldn’t take much at all. I guess this would be CoreYZ? Also, this is Creality which uses Marlin for their firmware. Chances are we will see this in Marlin in no time.

As far as ease of build, I suspect that’s not quite the case. The main thing I would worry about is the belt flexing under the print head. If you think about it, the nozzle only moves across the bed in a straight line, left to right. To print an object with a Y dimension you need to move the belt forward and back and depending on how you set up the line on which things are printed if there is flex there you won’t get bed adhesion. You could use the treadmill belt material coated with something that can be printed on. Or whatever belt sander belts are made of before the abrasive is glued on.