You can't programatically detect novel BS any more than you can programatically detect viruses or spam. You can only add the fingerprints of known badness into an ever-growing database. Viruses and spam are antagonistic to well-resourced institutions, and their databases get maintained reasonably well. LLM slop is being generated by those same well-resourced institutions. I don't think it fits into the same category as Nepenthes.

the extent to which a random string is a "theorem" of some system can be measured i am guessing.

ie, given some text, to what extent is it "grounded" in some sense in facts.