I think it's important to note that not all collisions are equally dangerous. Consider a sat on a polar orbit colliding with one on a equatorial orbit. Or two satellites on different directions. That is going to be spectacular. Otoh, these kind of collisions are unlikely and should be manageable by just assigning certain shells (say 5km) for every possible direction and orientation.

If two Starlink satellites collide that go roughly in the same direction, it's not exactly a huge problem.

I think the biggest issue is to coordinate this and potentially disallow some excentric orbits.