Assuming that a rail operation does not fall under FRA jurisdiction for whatever reason, consider the following:
1. The FRA has been expanding their definition of what they have jurisdiction over. They could very well assume authority over any "full sized" (vs. park or live steam) railroad operation offered to the public.
2. In the unfortunate event of a serious accident, what standards would be applied in the resulting lawsuit? A railroad that applied the intent of the FRA standards in practice and had written records to back a safety program up would fair far better in court than someone defending themselves by claiming "nothing applies to us".
Maybe it is time for TRAINS or the NG operators themselves develop a realistic safety standards to voluntarily follow, before the FRA or lawyers force one on them. Note that many of today's RR standards the FRA derived from or simply respects industry accociation requirements (AREA, AAR (old MC
, etc.)