Think Lurkin, even in that scenario you could just submarine swap so that Subway receives the Bitcoin without touching Lightning. As far as anyone can figure out (Including Subway), it's a non-lightning payment. There's no way to enforce, and the last 10 years of crypto have shown that Money Transmitter enforcement agencies are bubble boy jokes with no teeth (Before even the implementation of Lightning, Coin Join, Schnorr, Submarine swaps, etc). They're good in their bubble boy environment, but no match for the common cold.
