Is this genuinely a through ticket in the same sense as say Manchester-Seattle via Heathrow on BA? What happens if the train/plane is two hours late? Does SQ look after you?
Yes, it's all issued on one PNR, and one ticket number (presumably SQ's 618 stock). The rail segments are treated as flights.
That means a delay in one segment will trigger an automatic re-accomodation of the passenger on a new flight. (In practice, it'll be interesting to see how train delays are relayed to SQ, so they know you really were on a delayed train, not just trying to 'rebook' yourself to a later flight).
The system behind it has existed for a while, and travel agents have been able to use it, but this seems to be the first time it's been marketed directly to consumers.
Is this SQ's way of avoiding competition out of BRS from the EK,TK and QR's, given that there's no aircraft that can fly BRS-SIN from our little driveway.