I love all these armchair scientists...on both sides here.
What's poisonous to one species may not be toxic to another...who knows if the cures and borax are toxic. As well, most plastics etc are resistant to acid so who knows if indeed a roe bag can be digested...if not, can it be passed...if not passed is it harmful? Who knows....all I can tell you is that I haven't encountered any dead steelhead washed up on the river (after 15+ years of steelheading).
With so many unanswered questions, I think it is dangerous to propose fixes that may actually offer no benefit to the fish!?! After all, if they banned roe bags, then whats next, roe, pink worms, lead weights, etc, etc, etc.