That's easy. From juridical point, all software without liable owner except mentioned science/arts, will be prohibited in all businesses working at restricted markets.
For listed above, could add (cellular) communication companies, energy (electric or gas) companies, water pipes, and other infrastructure critical, medical, emergency services.
And from Democratic experience, ANYBODY could become steward, just need to claim responsibility and may be conduct some bureaucracy procedures to prove ability to be liable.
From this my conclusion, if NOBODY will claim to be steward for some software, it will automatically become prohibited for mentioned businesses.