I saw your post, but had nothing to contribute regarding hole size; it's ironic that my problem may have stemmed from the subject of your inquiry. As for the holes, I'd have to measure them carefully, as there is no documentation regarding these. I know from previous reading that the original MXUS 3000 V1 motors had holes that were way too large, and when fitted with brass washers, riders were able to put many KW through them, seemingly without incident.
I stopped by Grin yesterday and purchased some custom cut Sapim 13/14 stainless steel spokes to fit my wheel. These are the same spoke I originally used, and the motor is laced into an Alex DM18 rim. The folks at Grin also thought it unusual that my spokes would fail at the elbow but didn't attribute it to the hole size. The spokes broke off near but not on the elbows in every case. The shear points were no where near the area making contact with the hole. I inspected the spokes around the broken ones or signs of stress, but saw nothing obvious. It is possible that larger holes cause excessive bending at the elbow when the spoke is stressed by impact, and that the weakest points resulting from this bending are at the tops of the elbows?
I have some washers lying around with ~13 Ga centers. I may give them a try, but for now, I'd prefer to avoid a total re-lacing job.