Thanks! I thought I had heard of someone working on a corexy version a while ago. I'm not sure if it ever materialized. I think it would be an excellent upgrade. I'm still using mine in H-bot form almost 3 years later! I've mostly overcome the racking issues by using some LM8LUU bearings in a few places... still, a corexy version would be superior.
If you have a good idea for how to convert this design to corexy, I think it would be great. If not, I'd recommend getting 3x LM8LUU bearings to mostly eliminate the racking. If you plan ahead, you could also extend the axes ~10mm without having to modify any of the printed parts. That way you won't lose any of the print space with the longer bearings.
See this "thing" for the longer bearing holders: http://www.thingiverse.com/thing:560217
I might also have the mods I made to the gantry somewhere on my computer to accommodate LM8LUU. I'll dig around for the STLs.