I agree that the design of the base leaves a lot to be desired. I was thinking or incorporating a design similar to the Sphinx, and maybe removing the inside set of wheels to accommodate, but I'm not sure if that's giving up too much.
I uploaded the Sketchup file in 2017 format today. Note that it's not fully complete, there are a bunch of screws and stuff missing, and a few brackets. You can buy the Workbee End Plates here: WorkBee CNC Y C-Beam Lead Screw End plate set (seen at Openbuilds) | eBay And the 4 hole motor mount plates here: End Plate with 4 motor mounting holes for CNCs using C-Beam and 8 mm Thread Rod | eBay Or, you can contact Chris Laidlaw directly at [email protected]. MG
Re your comments about cutting corner joints etc, I have an XL build and just cut a slot in the spoiler, see Images sorry most of the images don't apply.