Given the extreme differences in badness per ton I'm not sure if that's a reasonable metric. Maybe instead we could mandate yucca mountain level storage for everything that hasn't been evaluated, and then let companies decide for themselves whether or not they will be making enough of the stuff to justify studying how to dispose of it more cheaply.
It might be possible to establish categories where if your molecule has XYZ properties it falls into this bucket. I think a category for really novel molecules that haven't been evaluated is a good idea with tight restrictions on how much can be produced.
There should also be a presumption that minor edits to known dangerous molecules should be presumed dangerous without testing.
