Right now I am waiting on 3mm drill rods. I got a ton of them from China pretty cheap, but the waiting is going to be insane. I have, however, completed the CoreXY stage. As soon as I get those rods, I'll be able to assemble the XY carriage and see if this thing will work.

I've changed the completely printed XY stage so the rods are lined up with the small 'pulleys' I'll be using:

That's a 3mm gap between two captive nuts. It couldn't have worked out better.