This topic keeps coming up and I agree that the existing implementation isn’t ideal. It seems that the problem is because the nut is performing 2 tasks right now, keeping the wheel attached AND setting the distance of the axle to the rail. So what if we isolated the functions? What if we added set screws that were drilled and tapped through the edges of the carriage plates? If we also use an M5 nylock nut behind the eccentric we can make the wheel attachment just “tight enough”, and adjust the eccentricity separately and lock it in place with the set screw.
It does the same thing essentially, but without the need for grub screws. By running the eccentric nut down to the head of the bolt, then using a nylock to attach the bolt on the other side, it gives you the freedom to adjust the eccentric nut without it also having to mechanically hold the bolt in place. That job goes to the nylock nut.