Very cool, I too have OCD about the wobbly backboard.
I was going to do one of 3 things.
1, Design a sling that goes under the motor and back onto the front of the backboard.
2, Copy the design with Fusion and send the file to be cut in thick Carbon fiber, no flex in that stuff!
3, Wait around till the alloy upgrade is available
The bearing it'self is next to zero, WAAAAY better than the poly wheels that the CR10 uses (axial bearings have issues with side load an play, when I had the CR10 I was driven batty with the bearing play)
The problem is the ACM, its stiff, but not stiff enough IMHO for direct extruder cradle duty.